14 THE PALM-STEM. 



The Palms are the more fitted to afford this evidence, since the plants not 

 only form one of the most natural families, but also manifest a very great 

 similarity, both in respect to their vegetation and their products. The same 

 conditions, deviation of form of the cells in nearly-allied plants, may also be 

 demonstrated in other no less natural families, for instance, in the Eerns. 



2. I did not find raphides or other crystals in the cells of any Palm-stem. 



The Palms have not a bark distinctly separate from the 

 subjacent parenchyma, and exhibiting a special growth, 

 such as occurs in Dicotelydonous trees ; but the outer 

 layers of the cellular tissue are remarkable, and therefore 

 deserve description. In the young condition they have 

 thin walls, and cannot be distinguished from the cells of 

 the subjacent fibrous layer ; in more advanced age, how- 

 ever, their walls are thicker, and become hard and brown. 

 In many species for example, in Calamus, in many 

 species of Geonema this layer remains very thin ; its cells 

 do not acquire such thick walls, and appear to retain their 

 vitality throughout the whole life of the plant. In other 

 species, on the contrary, the surface of which is subject to 

 destruction by atmospheric influence, as in Cocos, Elais, 

 the rind acquires a considerable thickness, and gradually 

 draws a portion of the fibrous layer into its circle. In 

 such case this is not of equal thickness at all points of 

 the circumference of the stem, but passes deeply into the 

 fibrous layer in particular places, while in other situa- 

 tions it is rather thin. Under these circumstances, the 

 inner layers of the rind inclose a portion of the fibrous 

 bundles, which is not usually the case. 



The epidermis exists in old age only in the cane-like 

 and calamoid stems ; in the rest, it is more or less de- 

 stroyed by the action of the weather. It consists of a 

 simple layer of minute cells. As a general rule, no sto- 

 mates occur in it, but they do exist scattered in Ehapis 

 flabelliformis. In Calamus, it consists of minute cells 

 elongated in the direction from without inward, and 

 forms a stony, brittle, shining layer. 



The different kinds of pubescence also come under 

 consideration as appendages of the rind and true cellular 



