MAINTENANCE OF A FREE PASSAGE FOR AQUEOUS VAPOUR. 



297 



Stomata, which are spread over the green tissue of stems and flattened shoots, 

 are frequently sunk in furrows, channels, and pits, in plants whose greatest activity 

 occurs in the short rainy season, and they are saved from wetting in this position 

 by the most varied contrivances. On the rocky shores of Lake Garda, and up over 

 the mountain slopes to the heights of Monte Baldo, grows Cytisus radiatus, a 

 shrub of unusual appearance (see tig. 69 i). Its branches only possess rudimentary 

 green leaves, and are themselves furnished with green tissue, which plays the same 

 role as that assigned to the mesophyll of the leaf-lamina in normal foliaceous plants. 



^K 



Fig. 67.— Over-arched Stomata of Australian Proteaceie. 



1 Vertical section through a leaf of Hakea fiorida. - Surface view of the same leaf ; x 320. 3 Vertical section of a leaf 

 of Protea melli/era. * Surf ace view of the same leaf ; x360. 



These green branches bear very numerous secondary branches inserted in decus- 

 sating pairs. On the secondary branches new shoots develop every spring exactly 

 similar in form, and arranged in the same manner. At the period when this 

 development is taking j^lace, the humidity in that part of the Southern Alps, to 

 which Monte Baldo belongs, is very great. In dull weather, rain and mist, or dew 

 in fine w^eather, deposit large quantities of water on the soil, and on the plants 

 covering it, particularly in the alpine region of the above-named mountains, on the 

 westerly slopes leading down to the lake, which are thickly clothed with the shrubs 

 in question. It is therefore important that the rod-like branches of this Cytisus 

 should be able to breathe and transpire without hindrance, and that the short time 

 during which the conditions for these vital transactions are favourable, should be 

 fully and wholly taken advantage of. Here again the point above all others to be 



