OI' IVXCCIIAKIS CKM.srKM.OIOES ()87 



and excessive dryness come to li^lit on an examination of the 

 anatoni}' and physiology of the plant. 



TllK I'J'I DERMAL SySTEM 



The protecti\e system of the plant is very well developed. 

 There is a considerable covering of wax over the whole plant 

 (cf. /'. g). In addition, the epidermal cells are cuticularized 

 both without and within ; and particularly in the younger por- 

 tions, the surface is covered with peculiar hairs, of which usually 

 only the end-cells project above the wax. The stomata are exserted 

 and are apparently sensitive. The wax is laid down in the form 

 of irregular plates fitted together into a sort of mosaic. In the 

 younger portions, to about '^-y cm. back of the tip, the waxy 

 covering is very thick, while the outer layers are shed in the form 

 of powdery scales. Its very ready solubility in ether indicates its 

 fatty nature. The ciitifi is present in a layer over the entire plant 

 even up to the very tip of the growing point, though, naturally, it 

 has less thickness here than in the older parts of the plant. The 

 surfaces of the leaves present on the lower parts of the plant are 

 more heavily cutinized than either the wings or the stem. 



The /lairs almost always arise in pairs from two adjacent epider- 

 mal cells. In most of the members of this family, as Vesque,* whose 

 observations have been confirmed by more recent investigators, 

 points out, two kinds of hairs are to be found : glandular hairs and 

 mechanical hairs. Both kinds are present in this plant. The gland- 

 hairs, which are composed of double series of from 3-5 cells each, 

 differ from those mentioned by Vesque and Solereder t in that all 

 but the end-cells contain chlorophyl. The cutin is but slightly 

 raised by the not very abundant secretion, the nature of which has 

 not been any more definitely determined than that it is odorless 

 and soluble in ether (/. 7). That the secretion of wax is to be 

 assigned to the epidermal cells in general, and not particularly to 

 these hairs, seems probable from the fact that few or none of the 

 hairs are to be found on the older portions of the plant, where, 

 nevertheless, the wax is abundant. 



* Vesque, T. Caract^res des * ■•" * Gamop6tales. Ann. Sci. Nat. Bot. VII. i : 

 183. 1885. 



t Solereder, H. Systematische Anatomic der Dikotyledonen. 51511'. 1899. 



