3-« 



LECTURE XIX. 



to assume that both in the assimilating chlorophyll-corpuscles and in the non- 

 assimilating starch-corpuscles, the material for the formation of starch consists of 

 sugar. This latter is conveyed to the starch-forming corpuscles of the organs 

 which do not assimilate : it is formed, on the other hand, in the assimilating 

 chlorophyll-corpuscles by assimilation. The question now remains, therefore, how 

 does the sugar itself arise by assimilation ? I hold it as probable, even now, that 

 in this process the proteid substance of the assimilating chlorophyll itself co- 

 operates, and undergoes a change. Whether it is right to claim, with Berthelot 

 and Kekuld (1861), formic acid or some other member of the formyl group as 

 the first product of assimilation, on account of its simple constitution, I hold as 

 at least very questionable ; and it has hitherto been proved by nothing. I lay 

 still less value on Pringsheim's so-called Hypochlorin ; a substance, the chemical 

 nature of which is not established, the genetic relation of which to the starch in 

 the chlorophyll is not known, and the significance of which for the processes 

 of growth has not been investigated. Hypochlorin appears to me, rather, to belong 

 to the same category as the INIyelin of the animal physiologists, with which the 

 latter likewise do not know what to do ^ 



At any rate, even after all the recent researches, the fact, which I established 

 twenty years ago, that the starch in the assimilating chlorophyll is to be regarded 

 as the first distinctly recognisable product of assimilation, remains unaltered. Even 

 then I left the way open for further knowledge, since I laid stress on the fact 

 that it was a matter of the first distinctly visible product, and that probably other 

 products, hitherto not distinctly recognisable however, precede the formation of 

 starch. Hence, even if as a matter of fact formyl aldehyde or vegetable myelin 

 (I mean Pringsheim's hypochlorin) were actually an earlier product of assimi- 

 lation, from which the starch is developed in the chlorophyll, which is not the 

 case, there would still not be the smallest item to alter in the statements which 

 I have made since 1862. 



Having learnt to understand the most important function of chlorophyll, I 

 will now complete the natural history of this remarkable body by a few passing 

 statements as to the rest of its behaviour in different phases of Hfe of the organs 

 of the plant. It has already been mentioned that leaves which develope from 

 the buds in the absence of light, with a few exceptions, produce the first 

 rudiments of chlorophyll-corpuscles, it is true, but these remain small and usually 

 yellow, and likewise that the green chlorophyll-corpuscles can increase in number 

 by division when the cells grow. 



I convinced myself, in 1863, by a detailed investigation of the changes which 

 take place in the assimilating parenchyma of leaves in Autumn, before their falP, 

 of the fact that a structure so valuable with reference to the life of the plant as 

 the chlorophyll-substance, is not destroyed and chemically decomposed at once, 



* With respect to Pringsheim's Hypochlorin, Pfeffer expresses himself in his ' Pflanzen- Physio- 

 logie^ (B. I, pp. 194, 195, and 209) in very measured terms, it is true, but still protesting and 

 dissentient. Pringsheim's treatise ' Ueber Lichtivirkiing und Chlorophyllfitnk/ion in der Pflanze" 

 (Jahrb. f. wiss. Bot., Bd. XII, p. 288) is thoroughly examined in Hansen's paper on the ' Geschichte 

 der Assimilationstheorie' (Arbeiten des bot. Inst, zu Würzburg, B. II, p. 606). 



2 Cf Sachs, ' Entleerung der Blätter im Herbst' (Flora, 1863, p. 200). 



