12 



HARD WICKE ' S S CIE NCE- G SSI P. 



which come into contact, clue to this folding back, 

 are apparently possessed of the power of uniting, and 

 thus forming the cavities seen in a longitudinal 

 section. The formation of these cavities is due to 

 the linear growth of the aborted leaf; the bending 

 back of the leaf first takes place, as just remarked, 

 when very young and small. Points, probably of 

 the raised ribs near the apex, are brought into 

 contact with other points near the base ; attachment 

 takes place, thus forming the first cavity ; the leaf, 

 by growth, increases in length, both between the 

 points of attachment and the apex, and the same 

 points and the base, which, afier proceeding a 

 certain distance, again come into contact and unite, 

 forming a second cavity, and so on (Fig. 7). A 

 transverse section reveals cavities that radiate from 

 the stem. These are probably caused by the uniting 

 of the underneath ribs of the leaf; for through each 

 partition wall, between the cavities, may be traced 

 the vascular bundles which ran through the ribs of 

 the leaf in its earlier history, and which are 

 continued through the base of the leaf into the 

 stem, as seen in the transverse and longitudinal 

 sections (Figs. 6 and 9). 



The cavities in the scale are sometimes separate 

 and distinct from each other, but more generally 

 several, or even all, are united, forming one large 

 cavity with deep recesses. 



The apex of the leaf or scale, folded back upon 

 the base, is never attached cell to cell, the tissue 

 here never being continuous. It is, however, in- 

 variably pressed quite close ; so close indeed, that 

 in the cavity of a fully-developed scale I have never 

 found any extraneous matter (I shall, however, refer 

 to a younger scale later on). Fig. 9 is a fair example 

 of the numerous scales I have examined. Hence, 

 though these cavities are not hermetically sealed by 

 cell-fusion, they may be considered practically air- 

 tight, and may thus be correctly termed enclosed 

 cavities, and, as such, they will render the stomata 

 useless. It must not, however, be forgotten that the 

 united cavities converge to the apex, which suggests 

 that some time in the past they were in communication 

 through an opening here, with the outer air ; and 

 also the probability of the stomata carrying on their 

 function in a gradually lessening degree, until the 

 opening was finally closed. 



With regard to the method of development of the 

 scales, I am at a loss to determine whether it is due 

 to a folding back, and attachment taking place as 

 described, or whether, after the folding back, caused 

 by the cells of the ribs not being developed at the 

 same speed as those of the lamina, has taken place, 

 these former are (subsequently) developed with a 

 speed equal to the growth of the lamina cells, and 

 continuity is thus preserved. This appears to me to 

 be a question presenting great difficulties, ss it is 

 highly probable that both methods obtain ; the first 

 in order being the method by attachment, gradually 



superseded by the continuous method, which latter 

 may be replaced in course of time, if needed, by the 

 production of the thick fleshy scale, without any 

 break in the continuity of its tissue from the stem. 



From these observations it will be seen that, which- 

 ever way the development of the scales may take 

 place, it is such that the stomata and glandular hairs 

 of a previous condition are enclosed in cavities, which 

 may, in the course of development, altogether dis- 

 appear, cell tissue taking their place. 



If it be true, that the leaves of L. squamaria 

 have become aborted as leaves, and developed into 



Fig. 6. — Transverse section of a fully-developed scale, showing 

 arrangement of cavities and vascular tissue. X 4. 



Fig. 7. — Longitudinal section of scale, illustrating the method 

 of the folding back of the lamina, and the formation thereby 

 of the longitudinal cavities. X 12. 



thick fleshy scales, it then follows that these scales 

 must have a definite function to perform, for it does 

 not appear feasible that such large and numerous 

 appendages should be retained and developed without 

 serving some purpose in the economy of the plant. 

 The primary function of these scales I believe to be 

 one of food-storage ; the attachments of the plant to 

 its host, as we shall presently see, while perhaps 

 numerous, and in some cases very complete, do not 

 seem sufficient to maintain the rapid growth of the 

 thick succulent stem, the comparatively large flowers, 

 and the production of the numerous seeds. The 



