24 ART. 10. — S. KUSAXO : STUDIES ON THE PARASITISM 



and elaborated materials through sieve-tubes ; while in Viscum 

 the absorption of food from the host is limited to crude materials 

 in aqueous solution. Quite recently Cannon 1 ' has ascertained also 

 the absence of sieve-tubes in the haustorium of Pkoradendron 

 villosum, a green parasite. Of course we can not establish the 

 physiology of nourishment merely from the structure of the 

 elements ; experiments are always necessary. 2) But as this investiga- 

 tion is beyond the scope of the present paper I will here confine 

 my remarks as to Buchleya to a description of the histological 

 structure of the cortical part. I have examined with great care 

 to ascertain whether the walls of any parenchymatous cells are 

 furnished with callus, which would prove them to be sieve-tubes. 

 After the process of Peiuce I have stained the sections from the 

 haustoria, collected in various periods, with an aqueous solution 

 of a'nilin-blue and examined them in glyceliue after washing with 

 water. A part of the bast of the mother-root was treated in the 

 same manner for the purpose of control. The presence of callus 

 was evidently proved in the mother-root, but never in the haus- 

 torium. The following facts are also in the favour of the view 

 that there are no sieve-tubes in the cortical part of the haus- 

 torium : — 



1). Throughout their life, the parenchymatous cells of the 

 cortex retain their nuclei, which are large and round or oval when 

 young but spindle-shaped when old. 



2). In these cells the slightly granular plasm accumulates 

 around the nuclei and forms plasmic strings, while, on the 

 contrary, in the sieve-tubes the plasm with granular contents is 

 to be found only adhering to the cell-wall. 



]). Cannon, loc. cit. 



2). See Pfeffer's remark in his Pflanzenphysiologie 1S97, Bd. I, 2 Anil. p. .".•">">. 



