1040 LIFE : OUTLINES OF GENERAL BIOLOGY 



for gophers are wonderfully instructive to the evolutionist. It's an 

 ill wind that blows nobody good! 



Lichen after Lichen. — ^An interesting study that finds many 

 illustrations is the succession of different forms of life in the same 

 place. We see this if we watch a clearing in the forest for a number 

 of years in succession. We see it if we make a careful study of the 

 sequence of living creatures in a hay infusion — one type following 

 another tiU nothing is left but water. The successive types or 

 associations of types do something to the environment that opens 

 the door to successors and, directly or indirectly, involves their own 

 exit. A good illustration has been recently disclosed by Mr. C. C. 

 Plitt, who has made a study of lichen succession. When we climb 

 a mountain above the region of grasses and mosses and Alpines, 

 we reach a lichen-vegetation clinging to the bare rocks and assisting 

 in the very beginning of soil-making. These lichens succeed in 

 gaining a livelihood where nothing else will live because they are 

 dual plants, as everyone knows — ^Algae in close mutually beneficial 

 partnership (or symbiosis) with Fungi. What neither plant could 

 do alone, they can do together. The^^ live and thrive, but they are 

 mostly of a closely clinging encrusting t3rpe. In less exposed places 

 the same substratum, whether rock or tree, shows a succession. 

 The crust ose species are succeeded by foliose species. Then there is 

 a struggle for existence between these, and the more loosely growing 

 forms with ascending margins replace those that cling very closely. 

 Later on, there arise fruticose species like the Reindeer Moss, sug- 

 gestive of miniature fruiting shrubs. The trunk of a tree sometimes 

 shows a prolonged succession of lichens, ending in the greyish 

 pendent Usnea having sole possession. This is one of the many 

 aspects of the Struggle for Existence. 



ACCLIMATISATION AND BIOTECHNICS 



Up to this point our discussion has been essentially biological, 

 though the human factor has none the less come in, and indeed 

 frequently. But in these times of ever-growing population, 

 and with rising standards of life as well, the questions of 

 Acclimatisation must increasingly range further and further 

 beyond our limited scientific inquiries, and become more 

 and more of regional, national, and thus worldwide importance. 

 Already this has become of increasing and active importance, as so 

 notably in Canada, for which the selective production of varieties 

 of wheat, capable of more and more rapid growth in the shortening 

 season as we go northward, has added and still goes on adding, vast 

 regions to the plough. In such cases, of course, we are going far 



