REPRODUCTION 275 



He quotes Delpino* as saying that in one part of Liguria 

 the plants of Viola odorata bear only the open flowers, 

 while near Turin both kinds occur on the same plant. Here 

 in California cleistogamous flowers are few, confined in the 

 main to the forests, the floor of which is but dimly lighted. 

 Is this because of the brilliancy of the sunshine? 



What are the advantages of sexual and non-sexual repro- 

 duction? Before it began to be shown at all that reproduc- 

 tion, like other functions, exhibits in its course the irrita^ 

 bility of the organism, sexual and non-sexual reproduction 

 were compared solely with regard to the species, the off- 

 spring, and the conditions in which they would find them- 

 selves when separated from the parent. For example, 

 Vaucheria produces resting spores by sexual means, immedi- 

 ately germinating zoospores by non-sexual means. When 

 the conditions are becoming less favorable for active vegeta^ 

 tion, and when active vegetation finally becomes impossible, 

 it is obviously to the advantage of the offspring and to the 

 species that the new individuals should be of such character 

 that they can withstand unfavorable influences for a time. 

 But between the advantage of forming resting-spores when 

 the conditions are to be unfavorable, and the means of 

 attaining this desirable end, there would be a great gap 

 had it not been shown that the influence of circumstances 

 upon the parents causes them to form resistant instead of 

 extremely sensitive reproductive bodies. There must be 

 some advantage to the parents, as well as to the offspring, 

 else they would not engage in sexual reproduction. Accord- 

 ing to circumstances, according to stimuli, according to the 

 advantage of the mature individuals, they will continue to 

 vegetate, or they will form non-sexual spores or vegetatively 

 produced individuals ( bulbs, runners, etc. ) , or they will 

 form new individuals by sexual means. In the orderly suc- 

 cession of events in nature, changes in the water-courses, in 

 the soil, and in the air normally precede a degree of heat, 

 dryness, or cold which suspends active vegetation. These 

 preliminary changes give the stimulus which cajuses plants 



* Delpino, F. SuU' Opera, la Distribuzione dei Seesi nelle Plante etc., 

 1867. 



