94 BOTANICAL GAZETTE [February 



thicker epidermal wall, is fully as successful in the struggle for 

 existence as V. Thapsus growing by its side, so thoroughly pro- 

 tected by an abundance of epidermal hairs. It is not difficult to 

 see that the woolly coating may be advantageous to young leaves, 

 just emerging from the bud ; but it is extremely difficult to find any 

 advantage in the few simple and stellate hairs scattered over the 

 leaves of Lepidium and Capsclla. 



Stomata 



In over two-thirds of all the plants studied the stomata were 

 found to be more abundant on stem than on rosette leaves. Some- 

 times this difference in number is only slight, but sometimes, as in 

 Mitella diphylla, Lepidium virginicum, Monarda punctata, Aquilcgia 

 canadensis, Campanula rotundifolia, Capsella Bursa- pa storis, and 

 Geum album, this difference is considerable. Stomata are also 

 most abundant on the lower side of the leaf. This is true of about 

 80 per cent of all the plants studied. This difference is most pro- 

 nounced in leaves that have their upper and lower sides well devel- 

 oped, such as the broad mesophytic rosette leaves. Narrow, 

 xerophytic stem leaves, such as have both sides almost equally 

 exposed to light and air, have approximately the same number of 

 stomata on both sides. The more xerophytic the leaves, the 

 greater are the number of stomata as compared with the corre- 

 sponding mesophytic leaves. As a rule, the size of stomata is 

 correlated with the number. The larger the number of stomata 

 on a given leaf surface the smaller they are. This was found to be 

 true in over 60 per cent of the specimens compared. Broad meso- 

 phytic rosette leaves have fewer but larger stomata on a given sur- 

 face than the corresponding narrower, more xerophytic stem leaves. 

 In these there is a larger number of stomata per unit surface, but 

 the stomata are decidedly smaller in size. 



There also seems to be a correlation between the number and 

 size of stomata, and the size of epidermal cells. The broad rosette 

 leaves have, as a rule, larger epidermal cells. With these larger 

 cells are associated fewer but larger stomata. 



Anterior-posterior orientation of stomata is noticeable in the 

 stem leaves of Campanula rotundifolia, Linaria canadensis, Arabis 



