296 



PHYSIOLOGY OF GROWTH AND CONFIGURATION 



sperms of the same species. Upon the sperms of other plants this substance 

 appears to have no effect. 



The reproduction of fungi is also influenced by a large number of external 

 conditions. 1 It is generally true that reproduction does not occur in algae 

 and fungi under conditions favorable to vegetative growth, while conditions 

 favoring reproduction usually retard vegetative growth. - 



Sexual consanguinity" is necessary for the union of the sexual cells of seed- 

 plants as well as of spore-plants. The chemotaxis of sperms (as of ferns) is 

 paralleled by the chemotropism of the pollen-tubes of flowering plants. Just as 



Fig. 171. — Germinating pollen-grains of \'aUota purpurea, their tubes direeted toward a mass 



of diastase. (After Lidforss.) 



the sperms swim toward the source of diffusion of the attracting substance (such 

 as malic acid), so do the pollen-tubes bend and elongate toward this source. 

 Fig. 171 shows a culture of pollen-tubes of Wjllola purpurea growing in a 30-per 

 cent, solution of sugar with gelatine enough to form a jell v. The dark area in the 

 center represents a mass of diastase, toward which the growing filaments are 

 attracted.' 



1 Klebs, Georg, Zur Physiologic der FortpBanzung finigcr Pilze. III. AUgeuiemo Betrachtungea. 

 Jahrb. wiss. Bot. 35 :• 80-203. rpoo. 



' Also, see: Jickeli, Karl, ¥., Die UnvoUkommenheit des Stoffwechsels als Veranlassung fiir Vermehrung, 

 jichsthum, DifFcrenzicrung, Ruckbildung und Tod der Lebewesen im Kampf urns Dasein. Berlin, 1902. 



* Lidforss, Bengt, Untersuchungen iiber die Reizbewegungen der PoUenschlfiuche. Zeitsch. Bot. IJ 

 443-496. 1909. 



• This and Die next following paragraph arc added from the 7th Russian edition. — EJ. 



