LATICIPEROUS TISSUE OV MANIHOT GLAZIOVII. 203 



distinct origin for the laticiferous cells, such as those of 

 Euphorbia, Jatropha or Hura, and for the laticiferous 

 vessels such as I found to occur in Manihot. That the one 

 form has been derived from the modification of the other is 

 improbable. The essential distinction between the two seems 

 to me to consist, not so much in the fact that the laticiferous 

 vessels are originally septate, while the cells are not so, as in 

 other phenomena of their development. The points on which 

 I am inclined to lay most weight are the following. The ves- 

 sels, except where they form protruding branches (which has 

 not been found to take place in Manihot), occupy from their 

 first origin the same position relatively to the surrounding 

 tissues as they maintain in the mature condition. The lati- 

 ciferous cells, on the other hand, are constantly, throughout 

 their whole period of development, forcing their way into new 

 regions, by penetrating between the ceils of the tissues which 

 surround them. This power of independent growth is univer- 

 sally characteristic of the laticiferous cells, and on it their entire 

 development depends. In the case of the vessels it only ap- 

 pears as an inconstant and secondary phenomenon, and, as 

 shown by cases like Chelidonium and jNIanihot, the complete 

 formation of the laticiferous system may take place without it. 

 A second point of distinction lies in the early differentiation 

 of the laticiferous system from all other tissues, which occurs in 

 the case of the cells only. As shown by Schmalhauseu (1. c), 

 small number of cells, already formed in the embryo, give rise a 

 to the entire laticiferous tissue of the plant (if that in the 

 secondary cortex be left out of consideration). This is not the 

 case with the vessels. It is true that here also we find the 

 rudiments of laticiferous vessels present in the embryo before 

 germination, but from these rudiments only an insignificant 

 fraction of the laticiferous tissue of the mature plant is derived. 

 Laticiferous elements are here constantly being formed anew 

 in the meristem of the various growing points as long as 

 ii-rowth ffoes on. In other words, the differentiation of the lati- 

 ciferous cells is simultaneous, while that of the vessels is 

 successive. 



