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518 MR. S. LE M. MOORE's STUDIES 



contain a considerable amount of proteid, though whether 

 proteid is still being manufactured in them I cannot say ; but in 

 the oldest cells which came under my observation were to be 

 seen numerous darkly-staining bodies which are most likely 

 nuclei. The branches are arranged in binary verticils, and the 

 basal cell of the branch being considerably younger than the cell 

 of the branch of higher order supporting it, has a smaller pit 

 than the latter cell and smaller stoppers. If the stoppers were 

 not present, what would be the necessary upshot ? The cell- 

 contents would w r ander from one part of the plant to another, the 

 main current flowing through the wider pit ; consequently the 

 main flow of proteid would be towards the tip of the main 

 branch, and the plant would tend to form a single, greatly 

 elongated thread. Of course, interposition of stoppers at the 

 pit's mouth of the basal cells of lower-order branches must 

 check the flow along such branches ; but the net result will be 

 equalization of the stream, and general distribution to all growing 

 points of the necessary proteids will thereby be ensured. • 



One may adduce several facts which seem to point to the existence 

 of a callolytic ferment in sieve-tubes. Thus the disappearance 

 of callus from the sieve- tubes of the rhizome of Phragmites com- 

 munis described by Janezewski* — disappearance caused by simply 

 placingthe rhizome in a warm chamber during early spring — strik- 

 ingly recalls the action of a ferment which is inoperative at low 

 temperatures. Again, Eussow f notes how in Pinus sylvestris and 

 other woody plants the callus dissolves, usually about two years 

 from the time of its formation, by a sort of corrosion, but in 

 certain of the tubes it may remain more or less unaltered, some- 

 times for teu years ; and there can be no doubt that side by side 

 with open sieves, others may occur completely blocked with callus J. 

 This one can readily understand by supposing that, for some 

 reason or other connected with the metabolism of the tubes or of 

 the coinpaniou cells, ferment has failed to make its appearance 

 in the cells with callus-closed sieves. Again, we know from 

 Russow's § researches, that the callus of sieve-tubes of fallen leaves 

 is not dissolved, and that small portions of starch also remain 

 behind || j the complete absence of callolytic ferment in the one 



» < 



Oomptes Rendus,' 1878. t Siteb. Dorpat. Naturf . Geseilscb. 1882. 



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X Wilhelm, Siebrobrenapparatt. § L. c* 

 | Briosi, Bot. Zeitung, 1873. 





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