DEVELOPMENT OF AHTICULATED LATICIFEIIOUS VESSELS. 137 



with fiivour, and it was still defended by writers of repute 

 as late as the year 1860.^ 



The investigations in question were chiefly carried out by 

 means of longitudinal sections through the growing point, 

 and embraced a large number of the plants which produce 

 latex, among which the Apocynese, Asclepiadeae, Urticaceee, 

 Euphorbiaceae, Papaveraceae, and Cichoriaceae were repre- 

 sented. 



Even the case of Chelidonium majus, where the remains 

 of the cross walls persist, as is well known, during the life 

 of the plant, seems at first not to have suggested any doubts 

 as to the correctness of the intercellular theory. The 

 question which was chiefly regarded in the researches of 

 this period was, whether the laticiferous vessels do or do not 

 possess a proper membrane from their first origin. It was 

 supposed at that time that two distinct lamellae of cell-wall 

 must exist between each two neighbouring cells of any 

 tissue, and when a double wall could net be detected 

 between a laticiferous canal and the neighbouring paren- 

 chymatous cells, it was considered a necessary inference 

 that the former had no cell-wall of its own at all. As soon 

 as Mohl, only a few years later, had shown that the original 

 wall between two neighbouring cells of a tissue is regularly 

 a single lamella, this ground for the intercellular theory 

 disappeared of itself. 



In the mean time Schacht,^ in 1851, brought forward an 

 entirely new theory, according to which the laticiferous 

 vessels generally ai-e *' laticiferous bast-cells, which are 

 frequently branched.^' He thus refused to regard these 

 vessels as forming an independent system, and wished to 

 include them as a subdivision in the Bast-cell group. And 

 here it must be remembered that Schacht and some other 

 phytotomists of that time were in the habit of giving the 

 name Bast to cells of the most different kind, if thick- 

 walled, long or branched, without any regard to their 

 position, just as in more recent times Schwendener has 

 extended the name Bast to elements of the most various 

 kinds which agree only in contributing to the mechanical 

 strength of the organs to which they belong. Schacht's 

 first researches extended to Euphorbia, Hoya, Rhizophora, 

 Chelidonium, Lactuca, &c. His view had the one advan- 

 tage over the intercellular theory, that he once more recog- 

 nised the cellular nature of the elements of which the 



' As, for example by Henfrey, ' Micrographic Dictionary,' art. " Latici- 

 ferous Tissue," 2ad ed. 



* 'Botanische Zeitung,' 1851, p. 513. 



