5IO Minnesota Plant Life. 



unfavorable cliances against it, in the outer world. Thus, for 

 each kind of living thing an hereditary rhythm comes to be 

 established. 



At first the number of individuals in a species may be few; 

 later, a climax may be reached in the maintenance of the spe- 

 cies, and following this the number of individuals may dwindle 

 until finally the species becomes altogether extinct. There is, 

 therefore, a "life of the species" distinct from the life of the 

 individual. For a species to maintain itself through the cen- 

 turies it must be strong — that is, composed of strong individ- 

 uals, each able to hold its own in the battle with other types of 

 life and with the forces of Nature. For this reason the ''in- 

 stinct of self-preservation" characterizes every living thing. A 

 species composed of negligent, apathetic or suicidal individuals 

 could not continue in competition with others in which the 

 opposite qualities were developed. Nevertheless, although the 

 instinct to live is universal among living things, the necessity 

 of death is c(iually universal and here one faces an extraordi- 

 nary dilemma. For the interests of the species, each individual 

 is placed in a contradictory position. Yet the apparently 

 irreconcilable situation is understood when it is observed that 

 while the passion for life, in an animal, serves to keep the 

 species strong, the death, also, of the animal, at the .end of a 

 definite life-period, serves precisely the same end ; since in this 

 manner the species may consist always of fresh, young and 

 vigorous organisms rather than in large part of those old, 

 decrepit or shattered. While in the sphere of the individual 

 there is no solution of the problem of life and death, it is 

 illuminated in the sphere of the species. Thus, death at the 

 end of an appointed life-period has been described by Weis- 

 mann as an ''acquired physiological trait," developed for the 

 advantage of the species as a whole and no less useful than the 

 instinct to live which characterizes each individual. 



Willi these conceptions in mind it may be understood how 

 a plant (m* animal species may be regarded as a continuous, 

 verv Iniigdived organism in which, in a rhythmical succession, 

 individuals constantly form and disintegrate. Possibly the liv- 

 ing substance of the 'species as a whole might be conceived of 

 as a sea in whicli that of the individual organisms was as the 



