SOME PLANT BIOGRAPHIES. 193 



if the fruit happens to settle on a light soil, al- 

 ready thickly covered with luxuriant vegetation, 

 it cannot compete against the established possess- 

 ors. But the winged fruits, being dispersed on 

 every side, enable many young plants to start 

 well in life on the poor stiff clays which best suit 

 the constitution of this riverside weed. The seed- 

 ling grows fast in such circumstances, and soon 

 produces large angular leaves, very broad and 

 thick, which in the adult plant have often a di- 

 ameter of five or six inches. They are green 

 above, where they catch the sunlight and devour 

 carbonic acid ; but underneath they are covered 

 with a thick white wool, which is there for a cu- 

 rious and interesting purpose. The damp clay 

 valleys and river glens where coltsfoot lives by 

 choice are filled till noon every day with mist and 

 vapour; and heavy dew is deposited there every 

 night through the summer season. Now, if this 

 dew were allowed to clog the evaporation pores 

 or stomata on the leaves of coltsfoot, the plant 

 would not be able to raise water or proceed with 

 its work except for perhaps a few hours daily. 

 To prevent this misfortune, the under side of the 

 leaves is thickly covered with a white coat of wool, 

 on which no dew forms, and off which water rolls 

 in little round drops, as you have seen it roll off a 

 serge table-cloth. By this ingenious device the 

 coltsfoot manages to keep its evaporation pores 

 dry and open, in spite of its damp and moisture- 

 laden situation. One may say, indeed, that every 

 point in the structure of every plant has thus 

 some special purpose; indeed, one large object of 

 the study of plants is to enable us to understand 

 and explain such hidden purposes in the economy 

 of nature. 

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