Ray Tracheids in Sequoia sempervirensAuthor(s): Marjorie GordonSource: New Phytologist, Vol. 11, No. 1 (Jan., 1912), pp. 1-6Published by: Wiley on behalf of the New Phytologist TrustStable URL: http://www.jstor.org/stable/2427020 .

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gEW P8YIOliOGIST. VOL. XI, No. I. JANUARY, 1912.

[PUBLISHED FEBRUARY 5TH.]

RAY TRACHEIDS IN SEQUOIA SEMPERVIRENS.

By MARJORIE GORDON.

[TEXT-FIGS. 1-7].

U NTIL recently it was thought that ray tracheids were absent from the genus Sequoia. Speaking of this genus Mayr in

1890 says: " die Markstrahlen bestehen durchaus aus Parenchym- zellen " (p. 271). In 1903, Jeffrey, in his special monograph on the Sequoias, makes no mention of ray tracheids. Gothan, in 1905, discovered ray tracheids in S. gigantca-"1 bei welcher species iibrigens in altem Holz auch hier und da Quertracheiden vorkom- men " (p. 848). Two years after Gothan's discovery, Penhallow, in the description of the genus in his text-book on the North American Gymnosperms (1907) states that the rays of the Sequoias are with- out tracheids (p. 223). Later, Jeffrey, in his article on Cunning- hamia sinensis (1908) speaks of the finding of ray tracheids by Gothan in S. gigantea and adds that they " have not yet been found in S. sempervirens " (p. 598).

The material for this investigation was from a museum specimen of the wood of S. sempervirens. From its external features it could not be seen whether it came from near the pith or from the outer part of the stem. The microscopic character of the annual ring, however, shows it to have been from an old portion of a stem: the annual rings are flat, and there is very little indication of a "6 middle " layer-a feature in which, as Gothan has shown, old stem and root-wood often agree (see Fig. 7). In this wood both marginal and interspersed ray tracheids were found.

The marginal ray tracheids are different in shape from the central parenchymatous ray cells. Fig. 1 shows a radially elongated ray tracheid which extends along the ray for a distance equal to the width of two-and-a-half spring tracheids, is about half as high as a central cell, and has a very irregular free margin. Often these

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2 MarMorie Gordon.

cells are considerably shorter than the one flgured. Pig. 2 shows a vertically elongated one. It also has a very irregular margin, but in radial extent covers only from one to otie-and-a-half tracheids, while in vertical extent it is fully twice as high as the parenchyma cells of the ray. The height of the latter is quite uniform, and the cells have also very regular walls.

These elongated marginal ray tracheids recall some of the structures found in the pine by Thompson (1910, Fig. 13), which structures he considered of a primitive type; and though in Sequoia no forms intermediate between the vertically elongated and the normal radially elongated ones were found, these vertically elongated structures are quite comparable to those of the pine, and are capable of a similar interpretation. Other marginal ray tracheids were found with sac-like projections from the end towards the cambium: these "' tailed " ray tracheids have also their counterpart in the pine, chiefly in young root-wood, where Thompson states that the tails "' seem to be due to an incomplete shortening of the tracheid as it turns along the ray " (p. 108), considered by him a vestigial feature in the process of ray tracheid formation from ordinary vertically arranged but short tracheary elements.

0 C) ~ ~ 2

Fig. 1. Fig. 2. These various forms of ilay tracheids occur on both sides of the

medullary rays, not forming a definite row, but scattered along the rays. Sometimes they are founid wholly in the spring wood (Fig. 3), but moi e often at the annual ring, the main part of the tracheid lying in the spring wood, but with a small part extending into the fall wood (Figs. 1 and 2).

The interspersed ray tracheids are similarly situated. Fig. 4 shows a radially elongated one. It extends over only one-and-a-half spring tracheids; but longer forms are quite common. Usually these cells are slightly less in height than the adjacent parenchyma cells (see Fig. 4). They are regular in outline, and although they closely resemble the ordinary ray cells in form, the pitting, as will be seen later, is very different. Fig. 5 shows two vei-tically

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Ray Tracheids in Sequoia sempervirens. 3

elongated ray tracheids. These vary in radial extent, are two to two-and-a-half times as high as the parenchymatous cells of the ray, and have irregular walls. They are similar to the " transitional "

tr-acheids of the young root and young stem of the pines (Thompson, 1910, Fig. 11). They do not, however, as in the latter group, give rise to the normal ray tracheids if the rays between which they occur separate farther, whereas in the pine this has been shown to be an ordinary method of formation of mar-ginal ray ti-acheids. Inasmuch, however, as they resenmble in form and position these so-called " transitionial " tracheids of the pines, they are of a primitive type.

There is thus in both marginal and interspersed ray ti-acheids of S. sempervirens much variability in form. Gothan (1905) has called attention to the variability in form of the r ay traclieids in the other species of Sequoia, which he compares to those of Picea and Larix, but which he states are not so abnormal as those of Thuja gigantea, as figured by Mayir (1890). Gothan, however, did not figure those of S. gigantea.

- ~~~~~~~~~

Fig. 3. Fig. 4.

So far we have described the ray tracheids from the standpoint of size and form, and have noted certain diffeiences in these featuLres between them and the parenchyma cells. These feattures, however, do not give us sufficiently definite and accurate data by which to distinguish the two constituents of the ray, and in practice the pitting was made the criterion. It affords a ready and absolutely reliable basis. The radial pitting is especially serviceable, as seen in face view in the radial sections, which were found most adapted to this study. The pits thus seen (Figs. 1-3) are quite small but rather variable in size. Ordinarily they are not more than half the diameter of those where a tracheid touches a parenchymatous ray cell. These in turtn are much smaller than the ordinary pits of the tracheids themselves (Figs. 2 and 3). In form, too, these three types of pits differ. The ordinary medullary r ay cell pit is oval, and its border is confined to the upper and lowe:- margins. This border

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4 Marjorie Gordon

is not so broad in proportion to the size of the pit, as is that of

either the ray tracheid or of the ordinary tracheid. The borders of the two latter also completely surtound the pores. The pits onl the horizontal and terminal walls of the medullary ray cells are cut across in the radial sections of the wood. The bordered (unilateral) character of the pitting on the ray tracheid as it appear s in section where it touches a parenchyma cell finally distinguishes this element from the simple pitted parenchyma cells of the ray. The appearance of such pitting is indicated in most of the figures (see Fig. 1, etc.).

~~~Q C1

Fig. 5.

Fig. 6.

Text-Figs. 1-6 x 225.

In line with both marginal and interspersed ray tracheids

parenchyma cells are sometimes found-similarly shaped, and also

scattered, as are the ray tracheids. Fig. 4 shows an interspersed ray tracheid which has to the left a parenchyma cell. Farther to

the left, beyond the figure, is a gap and then another ray tracheid. Immediately to the right of the ray tracheid figured is a also gap, after which there is another ray tracheid. Several series of inter-

spersed ray tracheids were followed towards the cambium and

invariably they disappeared and ultimately were not replaced by a row of parenchyma cells, but the two parenchymatous portions of

the ray simply came closer together and " pinched out " the tracheary elements. Pigure 6 shows a marginal ray tracheid, which has a

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Ray Tracheids int Sequoia semnpervi rens. 5

parenchyma cell in line with it, a consideirable distance to the left

(the intervening portion has been omitted in the drawing). This condition was quite freqUently observed. From the above des-

cription it will be seen that in Sequtoia the replacement of ray

tracheids by parenchyma is a very indefinite process, in contrast to

the pines, nor do the cells follow one another continuLously as in

the latter group. In the pines, where r eplacement is so definite, Professor

Penhallow, and later Thompson, consider-ed it indicative of tran-

sition between the elements, the latter clearly demonstrating that

the tracheai-y elemeent is the ancesti-al onie. The indications in the

transitional stlrLctures themselves are mUch better in S. seampervirenls

than in the pinies, sisple and bordered pits occUrring on the samle

elemnelt. These are present on the horizonital walls (see Fig. 2):

at the extreme left of the marginal cell is a bordered pit, then one

with a less distinct border, and so oni towards the right where there is an almiiost perfect simple pit, which is larger than anly of the

others. That the simple pits are r-eally simple and not bordered is

very clear, sinice the openinig is the samie width fr-omi top to bottom,

Fig, 7. Photograph of transverse sectioni of the wood of Sequtoia setmex- virens, showing por'tionis of four annual Xinzgs. x 37a5.

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6 Ray Tracheids in Sequoia sempervirens.

or wider at the top, whereas a border-ed pit, even if cut obliquely, would narrow towards the top. Mr. W. P. Thompson has found a similar feature in Abies (in press).

I have had access to fossil forms of Sequtoia loaned by Director Brock of the Geological Survey at Ottawa, and also to a type set of S. Penhallowii presented to Mr. I'hompson by Professor Jeffrey. No true ray tracheids were found. However, in S. Penhallowii Professor Jeffrey (1904) has noted that there are marginal cells which differ from the central cells in width, pitting, undulating borders, absence of tanniniferous contents, and presence of crystals (p. 327). Since the parenchymatous cells which replace the ray tracheids in S. serntervirens are quite different from the central cells in several of the features above mentioned, it is suggested that the marginal cells of S. Penhallowii may also be derivatives of ray tracheids.

The results of the present work have been to demonstrate the presence of ray tracheids, both marginal and interspersed, in old stem wood of S. sempervirents. This, in certain features of the structure of its annual ring, is comparable to root wood, and so of a primitive type. Gothan, to whom we owe our knowledge of this feature, compares such old stem wood of the pine to r-ootwood in another respect as well, the fewer resin canals which it contains, and so further suggests its primitive character. It is of interest that it is in this type of stemn-whichi, though old, yet retains primitive features-that ray tracheids have been found; and especially is it interesting since some of these ray tracheids are also of a primitive type. This feature makes it probable that wheti root wood is examined, or cer tain more primitive parts of the stem, ray tracheids will also be found. Since wounding appears to recall them in some forms (in Cunninghamia, Jeffrey, 1908, and Abies, Thompson, 1910) it would be interesting to know if such is the case here. No more material is available at present for further investigation, but it is thought desirable to publish these results at once, since the presence of ray tracheids in S. sempervirenis has so recently been denied, and since the occurrence of the two kinds of pitting on the one element affords such a clear demonstration that there is a transition between ray tiracheids and parenchyma.

It was on the suggestion of Mr. R. B. Thomson that this work was undertaken, and my heartiest thanks are due to him for his kindness and constant advice.

UNIVERSITY OF TORONTO, 1911.

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