94 



VII. TBICHOMES WAX. 



but rather radiate stellately in all directions. The cells of the 

 brown stars are connected together almost to the tip, and pro- 

 vided with living contents ; the nuclei in their interior can be 

 seen without difficulty. A cross-section through the leaf, where 

 it cuts a brown star centrally, shows that its stalk (Fig. 35, B) 

 is multicellular, and that not only the epidermis but also the cell- 

 layer next beneath passes over into it. 1 The stalk bears aloft the 

 stellate unilamellar but multicellular expansion. 



Should Shepherdia canadensis not be at our disposal, Elceay- 

 nus angustifolia can to a certain extent replace it. Here, on the 

 under side of the leaf, only the white air-containing scales are 

 present. The disk consists of cells either laterally isolated, or 

 grown together almost to the margin. 



B 



FIG. 35. Scales from the miderside of the leaf of Shepherdia caMO.densis. A, from 

 the surface ; B, in cross-section ( x 240). 



Prickles of Rosa. Now take a horizontal section through the 

 stem of a rose, say Rosa semperflorens of gardens, at the place 

 where one of the prickles arises. Try to halve the prickle as 

 nearly as possible in the middle, and then to take a thin section, 

 a process not so easy as it seems. In cutting, do not neglect 

 to moisten the cut surface with water. In a successful section it 

 can be seen that the epidermis of the stem is continued over the 

 prickle, the cells being at the same time more strongly thickened 

 and more elongated. Inside the epidermis there pass into the 



x This (as also Rosa, following) should preferably be classed as an 

 emergence, rather than a hair proper, since it includes also tissue of sub- 

 epidermal origin. [ED.] 



