THE CONVERSION OF THE PRODUCTS OF ASSIMILATION. HI 167 



corresponding dry weights and not on similar leaf areas. In io:)g. of dry 



substance he found as follows : — 



Total Nitrogenous matter. Proteid. Non-proteid. 



In the afternoon 3-537 3-199 0-338 



In the early morning 3-621 3-385 0236 



He concluded from these numbers that during the night a jorniation of proteid 

 from non-proteid (nitric acid and amides) took place, and that the total amount 

 of nitrogenous material increased. This conclusion does not appear to us to 

 be sound. We will attempt to reduce his determinations to a calculation of 

 similar leaf surfaces, using as a basis the values which Sachs obtained for the 

 loss in weight during the night of the leaves of Helianthus and Cucurbita : — 



Evening. Morning. 



I sq. m. Helianthus (dry) weighs 80-44 g. 70-80 g. 



I sq. m. Cucurbita (dry) weighs 59-92 g. 51-22 g. 



Total 14036 g. I22-02g. 



On an average one sq. m. of dry leaf substance 70-00 g. 61.00 g. 



If 70 g. of dry leaf substance in the evening represent the same leaf area as 

 61 g. in the morning, then 100 g. in the evening will be represented by 87 g. in 

 the morning ; in other words, a definite area of leaf blade loses 13 per cent, of 

 its dry weight during the night by translocation of the products of assimila- 

 tion. If we assume for the vine in Kosutany's researches a loss of only 10 per 

 cent., to use round numbers, then 100 g. in the afternoon would correspond 

 to 90 g. in the morning. We might then rewrite Kosutany's tables, for similar 

 leaf surfaces, in the following way : — 



Total Nitrogenous r> ^ -j m ,. -j 



matter. Proteid. Non-proteid. 



A definite leaf area contains in the afternoon 3-539 3-199 o-ssB 



The same leaf area contains in the morning 3-259 3-047 o-2ia 



From such a calculation it would be possible to deduce conclusions as to 

 the migration of nitrogenous substance during the night, and not as to its 

 increase in the individual leaf. An experimental confirmation of our argument, 

 resting as it does on a somewhat insecure basis, would be certainly of value. 



We have to note as well that, in addition to this daily translocation, another 

 transference of nutritive material occasionally takes place from the leaf. In 

 the first place, the leaves of evergreens frequently act as storehouses of reserve 

 and empty themselves in spring, just as do the cotyledons of a seedling ; 

 before it dies, however, certain bodies migrate out of the leaf back into the 

 permanent living parts of the plant. This transference of material was for long 

 greatly overestimated, until Wehmer (1892) pointed out that it was in no way 

 substantiated by facts. More recently Ramann (1898) has demonstrated in 

 forest trees, and Fruwirth and Zielstorff (1901) in hops, that, as a matter 

 of fact, nitrogen, phosphoric acid, and potassium do migrate from the leaves 

 in autumn. This translocation can scarcely, however, be considered of much 

 importance ; this brief reference to the subject must therefore suffice. 



We need not pause here to give in detail the evidence for the translocation 

 of materials from other storehouses ; we have had other opportunities of 

 considering the subject, at least in part, and, in the course of our further 

 investigation, we will return to the subject when we study the causes of trans- 

 location in greater detail and the path by which the translocation products move. 



In the first place, we may consider certain purely -physical causes of trans- 

 location. We have already, in speaking of germination, and in the discussion 

 of the researches of Hansteen and Puriewitsch, drawn attention to one 

 fundamental principle of every translocation, viz. diffusion. It is quite im- 

 material whether the diffusion takes place from one cell to another or from the 

 cell to the exterior ; all that is necessary for the initiation of diffusion is that the 



