418 HOFMEISTER, ON 



rounded by a firm cell-wall, and separated from the ripper, 

 very delicate-walled, larger un-nucleated portion of the cell. 

 Corpuscula from the same tree examined one or two days 

 later, exhibited this small lower daughter-cell attached to 

 the lower part of the corpusculum, to whose walls the 

 lateral surfaces also of the upper, un-nucleated, larger 

 portion of the cell adhere, whilst the boundary in the 

 direction of the apex of the corpusculum becomes in- 

 distinct (PL LX, fig. 10). As in Pinus canadensis the end 

 of the pollen-tube during these processes exhibits no 

 opening ; its contents are of the same nature as in the 

 species just mentioned. The unimpregnated germinal vesi- 

 cles which fill the cavity of the corpusculum remain at 

 first unaltered, which is also in accordance with Pinus 

 canadensis. A difference, however, exists in Pinus sylvestris, 

 viz., that very often one or two of the germinal vesicles 

 which lie in the micropylar end of the corpusculum and 

 touch the end of the pollen-tube, have firm membranes 

 composed of cellulose, a fact which has never been observed 

 in Pinus canadensis. After the cell which is pressed into 

 the lower end of the corpusculum has become changed by 

 repeated divisions into the compound pro-embryo, the tip 

 of the pollen-tube of Pinus sylvestris often appears to be 

 open, and its contents to be discharged into the cavity of 

 the corpusculum ; this is plainly the result of mechanical 

 rupture. The cells of the endosperm which surround the 

 funnel-shaped depression leading to the corpusculum 

 expand considerably in width after impregnation, and 

 compress the pollen-tube, frequently to such an extent as 

 to obliterate the cavitv of the latter. Its contents thus 

 undergo a strong pressure, which must ultimately lead to 

 the rupture of the free end. 



In Pinus abies, L. [Abies excelsa, D. C), I observed 

 phenomena similar to those in Pinus sylvestris. In 

 some cases I saw the daughter-cell of the corpusculum 

 after the former had grown to a large size, and its 

 contents had increased and become firmer in immediate 

 contact with the end of the pollen-tube (PI. LXI, fig. 1). 

 In others I found a similar but very large cell half way 

 towards the base of the corpusculum divided into four 



