REPRODUCTION 277 



wholly incapable of reproducing themselves by sexual means. 

 The bacteria, the higher fungi, and many independent 

 plants illustrate this. Some of the higher algae, archegoni- 

 ates, and flowering plants may go on indefinitely, without 

 reproducing themselves by other than purely vegetative 

 means, and with no evidence of injury to the individual or 

 to the species. It is only when special conditions produce 

 special effects on plants, that they need to reproduce them- 

 selves by sexual or non-sexual spores. Under special con- 

 ditions, reproduction becomes a necessity by becoming 

 advantageous to the individual. The species profits ac- 

 cordingly. 



Certain advantages to the species are conceivable in the 

 spore method of reproduction over any vegetative method, 

 and certain advantages are conceivable in the sexually 

 produced offspring over those non-sexually produced, but 

 these are conceptions rather than proved facts in all but a 

 very few cases. These few cases may or may not be typical 

 of the majority. It is conceivable, for example, that the 

 formation of new individuals by runners, as in the straw- 

 berry, and by suckers, as in the coast red-wood (Sequoia 

 .semper virens), is advantageous to the species. The new 

 individuals hold the territory won by their parents and 

 may even extend it somewhat. The young are nourished 

 by the parent until they have attained size, strength, and 

 development which give them an advantage in competing 

 with other plants for space and for the means of existence. 

 These means of reproduction are, however, defective in 

 that they do not secure the dispersal of the new individuals 

 and consequently do not tend to insure the survival of 

 the species or to extend its territory rapidly enough. The 

 survival of the well-equipped offspring formed by vegetative 

 means is certain so long as the conditions in the space 

 occupied by the parent remain favorable, but such repro- 

 duction is dangerous, because wide dispersal will secure for 

 the species some positions at least in which it can be main- 

 tained whatever may befall individuals in other places. 

 A puddle may become densely populated through the vege- 

 tative reproduction of the algae and animals started there- 



