24 | Raymond John Pool 
able only by the development of a greater number of stomata. 
The increased number of stomata would tend to bring about a 
greater loss of water from the plant by transpiration which could 
only be offset by a great increase of absorbing area at the roots 
together with the development of a greater number of conducting 
channels, both of which points are abundantly proved. The thick 
cuticle certainly prevents water-loss directly through the epi- 
dermis. The greater development, of fibrous tissue in the dry 
form might indicate that this was for support, but why such a 
need for increased support? The dry form was scarcely larger 
than the moist form, and, if anything, the latter was exposed to 
wind and other forces more directly than was-the form among 
the Artemisia plants. The whole process is a very slow one, and 
the exact sequence of events, together with the factors directly 
concerned, could be proved only by control cultures. 
“Water Storage Tissue.” 
In this study whenever structures were found which corre- 
sponded to those cells or tissues commonly called “storage” cells 
or tissues, I have not hesitated to so designate them. I am aware, 
however, of the fact that this whole question is still a more or 
less open one. Although the great majority of the plants in this 
study show more or less well-developed structures of this kind, 
we must still exercise considerable reserve in attempting to ex- 
plain the full significance of “water storage cells.” Perhaps this 
character is more universally present in plants of arid or desert 
habitats where the holard is very low; yet it is also present in a — 
* number of plants which inhabit swamps and indeed moist tropical 
jungles. It is developed in many unrelated families so that it 
bears no apparent connection with phylogenetic affinity. The ex- 
act significance, then, of these structures has not been demon- 
strated, and it is imperative that some one should take the prob- 
lem in hand and work it out so that all doubt or controversy is 
removed and the true nature of “storage cells” is determined. 
All through this investigation I have noted that these cells retain 
the stains very tenaciously after the contiguous cells or tissues 
have been perfectly cleared. This shows that their power of re-- 
tention of stains is marked, but whether they exercise the same 
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