72 DIFFUSION AND OSMOTIC PRESSURE 



the roots of maize seedlings, and a similar phenomenon is 

 very commonly met with in the case of bacteria, yeast fungi, 

 etc. Molisch l believed this to be generally true, but Czapek 2 

 has shown that he was probably mistaken. The latter found 

 that normal roots give off not only CO 2 but also phosphoric 

 acid in the form of an acid salt. These substances must of 

 course pass out through the protoplasm. There seems to be 

 no doubt from the work of Dandeno 3 that both organic and 

 inorganic substances will diffuse out from the cells of foliage 

 leaves if these are kept covered with water. In these cases 

 inward and outward diffusion seem to take place in exactly 

 the same manner. 



It is a well-known fact that enzymes, especially diastase, 

 pass out from the cells of embryos and digest food stored in 

 the endosperm of seeds. 4 This argues the permeability of 

 the protoplasm of both embryo and endosperm to these 

 substances. In this connection evidence has also been 

 presented that the cells of embryo and endosperm are both 

 permeable to carbohydrates, probably of the glucose group. 

 Whether these arise from the action of an enzyme derived 

 from the embryo, or from the action of enzymes formed 

 within the endosperm itself, 5 is of no consequence so far as 

 permeability is concerned; after the carbohydrates are 

 formed they diffuse into the embryo. 



h) Variations in permeability. If a turgid cell gives 



1 H. MOLISCH, " Ueber Wurzelausscheidungen und deren Einwirkung auf orga- 

 nische Substanzen," Sitzungsber. d. kais. Akad. d. Wiss. zu Wien, math.-nat. hist. 

 Klasse, Vol. XCVI (1887), pp. 84-109. 



2F. CZAPEK, "Zur Lehre von den Wurzelausscheidungen," Jahrb.f. wiss. Bot., 

 Vol. XXIX, pp. 321-90. 



3Loc.cit.,p.ll. 



*GBUSS, " Ueber d. Eintritt von Diastase in d. Endosperm.," Ber. d. deutsch. bot. 

 Ges. zu Berlin, Vol. IV (1893), p. 286; also B. HANSTEEN, "Ueber die Ursachen 

 der Entleerung der Reservestoffe aus Samen," Flora, Vol. LXXIX (1894), pp. 419-29. 



5 K. PURIEWITCH, "Ueber die selbstthatige Entleerung der Reservestoffbehalter," 

 Ber. d. deutsch. bot. Ges., Vol. XIV (1896), pp. 207-15; IDEM, " Physiologische Unter- 

 suchungen fiber die Entleerung der Reservestoffbehalter," Jahrb. f. wiss. Bot., Vol. 

 XXXI (1897), pp. 1-76. 



