430 HOFMEISTKR, ON 



accumulations of gelatinous matter are found on the outer 

 walls of these cells (PI. LXII, fig. 8). 



I have never seen the pollen-tube ramify in the Abietineae. 

 Each pollen-grain sends forth only one tube; if several 

 corpuscula of the same ovule are to be impregnated, it is 

 indispensable that several pollen-tubes should reach the 

 nucleus. There is no ground for assuming an incapacity 

 for impregnation in any of the different corpuscula of the 

 same endosperm. The impregnation of all the corpuscula 

 of one endosperm, when not exceeding three in number, 

 happens not unfrequently m Pinus sylvestris and canadensis, 

 each being acted upon by a special pollen-tube. In Taxus 

 the impregnation of several corpuscula by the very widely 

 expanded end of a single pollen -tube, is of very frequent 

 occurrence ; and in Juniperus and Thuja it is the rule. 



The impregnated germinal vesicle of Taxus baccata 

 and canadensis divides frequently by longitudinal septa 

 before any increase takes place in the number of 

 its cells in a longitudinal direction. The pro-embryo 

 not unfrequently consists of only four longitudinal rows" 

 of cells, but usually of six (PI. LXIII, fig. 12). In 

 the longitudinal development of the pro-embryo its rows 

 of cells behave very differently. In some, multiplica- 

 tion and growth cease at a very early period ; it usually 

 happens that the upper end of the pro-embryo exhibits 

 some three-sided cells which renew themselves rapidly 

 downwards, and belong to no one of the longitudinal 

 rows underneath, of which the pro-embryo is composed. 

 Very commonly two or one of the longitudinal rows of cells 

 immediately adjoining the longitudinal axis of the pro- 

 embryo are more vigorously developed and multiply their 

 cells in a longitudinal direction more rapidly, than the 

 cells nearer to the periphery (PI. LXIII, fig. 13). The 

 pro-embryo does not break up into single rows of cells 

 until a later period, and then usually only partially. Nor- 

 mally one only of them goes beyond the first commence- 

 ment of embryo-formation.* 



* ' Hartig zur Entwickelungsgesch. d. Pflanzen,' Leipzig, 1844, fig. 25, and 

 Schacht (1. c. pi. ix, figs. 11, 13) represent the first stage of development of 

 the pro-embryo as an oval mass of parencbymatal cellular tissue. I cannot 

 confirm this ; the pro-embryo appeared to me, even in its earliest youth, to be 

 always clearly composed of longitudinal rows of cells. 



