212 



The Plant World. 



highly suggestive and well worthy of being put to the test of 

 extended investigation. This is especially true of the closing 

 paragraphs, which are avowedly speculative, but which none 

 the less can not be ignored. It seems, so the author puts it, that 

 there is ground for maintaining that intolerant trees are on the 

 whole those best fitted to endure deprivation of moisture. Is 

 not a thin foliaged tree one which has adapted itself to meagre 

 conditions^ Given an abundance of light, moisture, heat and 

 plant food, and full-foliaged trees ought to develop, just as 

 heavy feeding and generally favorable conditions tend to breed 

 heavy stock. Reduce the supply of any one of these necessities 

 of plant life to a point below the needs of the organism at the 

 summit of activity, and the plant will no longer need the same 

 leaf area. Cold climates, poor soils, and desert regions are the 

 homes of the narrow-leaved and sparsely -foliaged broad-leaf 

 trees. Drouth-enduring vegetation is characterized by an ex- 

 cessively small green surface. The plant has perforce adjusted 

 itself to starvation conditions. A similar adjustment naturally 

 follows subjection to low summer temperatures or poor soils In 

 other words, pioneer, high -latitude, and xerophy tic vegetation does 

 not need and does not develop a great expanse of leaf surface. 

 Survival is not a question of being able to keep a place in a 

 crowded forest under deficient light conditions — of light they 

 have more than they can use. Hence xerophytic and pioneer 

 trees naturally become relatively intolerant. They can not suc- 

 ceed in association with the tolerant trees developed on rich, 

 moist soils and in a warm climate — climax species — because, 

 though they can endure deprivation along these lines better than 

 the climax trees, they are not fitted to endure deprivation of 

 light. Thus is explained the fact that intolerant trees are com- 

 monly found on poor and dry soils, a fact extremely inconven- 

 ient for the theory that what we have been taught to regard as 

 intolerance is really inability to compete with other species for 

 soil moisture. 



In Vol. IV, No. 1, of the same publication, Frederic f£. 

 Clements presents a paper on Plant Formations and Forest Types, 

 which, although it embodies principles already set forth in pre- 

 vious writings of the author, brings out so clearly and directly 



