EIGHTH LECTURE. 



THE INFLUENCE OF EXTERNAL CONDITIONS 

 ON PLANT LIFE. 



w. p. WILSON. 



IF you open your eyes and look carefully about, as you are 

 traveling from place to place, you will easily see that there 

 are very many differences between the plants of one region 

 and those of another. In the high mountains you will find 

 many thick-leaved plants, such as the Rhododendrons and 

 Sedums, and quite a number of peculiar forms not seen lower 

 down. Many of these may have a stunted, gnarly or dwarfed 

 look, quite strange to the vegetation at the sea level. In still 

 another region the plants may have lost much of their natural 

 grace and beauty of form. They may look rigid and stiff, with 

 small thickened leaves or none, with short thickened stems, or 

 round and consolidated forms such as we find in the Cacti or 

 Euphorbias. These are the tenants of desert regions. 



Again, if you happen to go south into the tropics, sheltered 

 and shaded by immense thin-leaved trees, with the waving 

 green of the palm and the vine, you will find dense masses 

 and banks of dark green foliage belonging to Ferns and Sella- 

 ginellas, with climbing plants of various kinds intermingled. 



About your own door may be quite as interesting forms as 

 in more remote districts, only you are accustomed to them and 

 do not see their peculiarities. You may look out on pines and 

 oaks, on a great diversity of small plants, with the Indian. pipe, 

 a partial parasite, and a few ferns which can bear more wind 

 and cold than most of their relatives, plenty of mosses and 

 lichens, and, in fact, representatives of all the great plant 

 families. 



