42 A HOFMEISTER, ON 



corpusculum (PI. LXIV, fig. 1). The unimpregnated 

 germinal vesicles remain still unchanged in the upper 

 part of the corpusculum..* Sometimes one or two of the 

 impregnated germinal vesicles which are in contact with 

 the pollen-tube become clothed with firm cellulose mem- 

 branes, and adhere to the apex of the tube. 



The side-walls of the upper end of the corpuscula of 

 Thuja orientalis, Juniper us communis, and J. sabina are 

 considerably thickened, and furnished with delicate an- 

 nular ridges, which are often very clearly visible in the 

 form of transverse stripes. At the beginning of July the 

 contents of the corpuscula consist, as has been mentioned, 

 of very finely granular almost glass-like transparent pro- 

 toplasm in the middle of which a large vacuole occurs. 

 Above this vacuole the primary spherical nucleus of the 

 corpusculum lies embedded in the protoplasm. This nu- 

 cleus afterwards disappears, and in its place some new free 

 nuclei make their appearance, around which, in a short 

 time, spherical cells are formed, which are the germinal 

 vesicles. Whilst the latter continue to grow, the central 

 vacuole becomes perpetually smaller and smaller : at last 

 it disappears altogether, and the corpusculum is filled with 

 a uniform mass of protoplasm having the germinal vesi- 

 cles floating in it. Amongst the latter, one or more near 

 the upper end of the corpusculum are distinguished by 

 their great size (PL LXV, fig. 9 on the right). 



The pollen-tube breaks through the softened membrane 

 of the embryo-sac— which membrane extends over the 

 depression at the top of the endosperm — and becomes 

 swollen so as to entirely fill the depression. In the regular 

 course of things a large spherical cell now appears in the 

 interior of the pollen-tube, filled with granular mucilage 

 which surrounds a central transparent nucleus (PL LXV, 

 fig. 9). In certain conditions which must doubtless be 

 looked upon as more advanced, this cell has the form 

 of an ellipsoid, and is furnished with two nuclei, one in 

 each focus ; other conditions again exhibit the cavity of 

 the cell traversed by a septum passing between the two 



* A decisive proof that the pollen-tube does not, as Schacht supposes, en- 

 tirely fill the corpusculum ('Flora,' 1855). 



