I INTEODUCTIOX 25 



as the Daisy, have broad horizontal leaves ; while grasses 

 have more or less upright and narrow ones. The 

 Plantain and Drosera give good illustrations. Flantago 

 media and Drosera rotnndifolia have broad flat 

 leaves ; while in Plantago lanceolata and Drosera 

 anglica they are narrow and upright. 



Hairs on plants fulfil numerous functions : they 

 prevent undue transpiration, hence the hairiness of so 

 many species of hot dry countries, as the Riviera ; they 

 also protect the plant from too brilliant sunshine ; 

 again, they keep moisture from clogging the stomata, 

 or breathing pores, and are thus useful in cold foggy 

 districts, as, for instance, our northern heaths and 

 moors. Such hairs are dry and contain air ; but another 

 sort are juicy and conduct or even themselves absorb 

 moisture, as, for instance, is said to be the case with 

 those on the Chickweed. In some cases hairs protect 

 plants from being eaten by browsing quadrupeds, and in 

 many they prevent ants and other creeping insects from 

 obtaining access to the flowers and robbing them of their 

 honey. Hairs intended to perform this function are 

 often rendered more effective by pointing downwards. 



Water plants and those living in damp localities 

 have no need of hairs and are glabrous. Some species, 

 such as Silene infiata and Polygonum amphibin/m, are 

 glabrous in damp, and hairy in dry places. Their leaves 

 •are also much cut up, often into long linear segments. 



I have suggested^ that the object of this is to expose 

 as large a surface as possible to the action of the water. 

 We know that the gills of fish consist of a number 

 of thin plates, which while in water float apart, but 

 have not sufficient consistence to support even their own 

 weight, much less any external force, and consequently 

 collapse in air. The same thing happens with these thin, 

 finely -cut leaves. In still water they afford the greatest 

 possible extent of surface with the least expenditure of 

 effort in the formation of skeleton. This is, I believe, 

 the explanation of the prevalence of this form in sub- 



^ Flowers, Fruits, and Leaves. 



