608 CONSERVAT1VK ORGANS. [ LECT - XI - 



plants, they are observed on the inferior disk only ; 

 but in others, particularly in the Grasses, the Coro- 

 nariae, and the Palms, they occupy both surfaces. 

 Some Phytologists have asserted that the lower 

 tribes of plants are destitute of pores; but this 

 statement is incorrect, as they are easily demon- 

 strated in Marchantia and a few of the Mosses. 

 Plants which have no leaves, such as the Cactus 

 tribe and many of the Rushes, and some of 

 those, also, which have leaves, as the Grasses, 

 have pores on the stem ; but in general they are 

 confined to the leaves. Those leaves, however, of 

 aquatic plants which are constantly under water 

 are destitute of pores ; the upper disk only of 

 leaves which float on the surface of water possess 

 them ; and when a land plant is made to grow 

 under water, the new leaves, which are evolved 

 under the water, have no pores, although those 

 which they have succeeded, or the aerial leaves, 

 were furnished with them. Even in plants which 

 are partly emersed and partly submersed, as for 

 instance Ranunculus aquaticus, the leaves that 

 grow under the water are destitute of pores, while 

 those which float, or are above that fluid, are pro- 

 vided with them. It has, also, been asserted that 

 etiolated leaves, or such as are excluded from 

 the light, are destitute of pores ; but there is some 

 inaccuracy in this remark, as I have found them 

 as numerous on the interior etiolated, as on 



