164 MEMORANDA. 



and a few are without colour. These hairs average about the 

 l-55th part of an inch in length, by the l-490th of an inch 

 in breadth. There are seen scattered over the surface, in 

 addition to the hairs, numerous round cells, precisely similar 

 to those which form the bases of the hairs ; these apparently 

 indicate non-developed hairs. The arrangement of these cells 

 (taking together those which form the basis of hairs and those 

 whose hairs are abortive) is so strikingly similar to the 

 arrangement of the stomata on the opposite surface of the leaf, 

 as to suggest the question whether tliese cells are not homo- 

 logous with the stomata ; are in fact the cells fiom which 

 stomata would be evolved if they were produced. This idea 

 is strengthened by the fact that a trace of chlorophyll is seen 

 in these cells, while it is entirely absent in the ordinary 

 epidermal cells, but present in well-defined globules in the 

 cells of the true stomata. Whatever be the homological 

 relationship between the hairs and the stomata, there can be 

 no doubt that the cells to which I have alluded represent un- 

 developed hairs ; and, indeed, Dr. Lankester has long ago 

 shown the tendency to non-development of hairs on aquatic 

 plants, such, for example, as in the case of Callitriche, where 

 peculiar rosette-shaped cells in the epidermis represent non- 

 developed hairs. 



If a portion of the leaf of the plant be held between the eye 

 and the light, it will be seen that the thinner parts are per- 

 forated with numerous minute holes ; indeed these are dis- 

 tributed more or less over the whole leaf, excepting those 

 parts occupied by the ribs. The nature of these openings, 

 and their purpose in the economy of the plant, have given 

 rise to some speculation. Hooker describes them thus: — 

 " Conspicuously may be seen the numerous pores or stomata ; 

 these are circular, generally margined with red, and apparently 

 formed of a thin membrane, surrounded by a circle of red 

 cells," and Fitch's drawing shows a membrane stretched across 

 the pore. This is only the case, however, in the early con- 

 dition of the leaf ; at maturity, the thin pellicle disappears, 

 leaving an actual perforation, measuring in the specimens I 

 examined the l-84th part of an inch across. The develop- 

 ment of these pores has been carefully described by Planchon, 

 who has given them the name of Stomatodes, and subse- 

 quently by Trecul. Planchon believes that they are designed 

 to permit the escape of gases which are disengaged from the 

 Avater, and would otherwise collect in the spaces formed 

 between the ribs and the under-surface of the leaf. It appears 

 to me, however, that they might with equal propriety be 

 regarded as intended to drain off the superfluous water which, 



