THE HIGHER CRYPTOGAMIA. 425 



nuclei. Ultimately, and shortly before the pollen-tubes 

 penetrate into the rosettes of the corpuscula, two spherical 

 cells of the kind above mentioned (PI. LXV, fig. 9 on the 

 left) are often found in the tube, which in all probability 

 are produced by the division of the original single cell. 

 The increasing pollen-tube now presses together the ro- 

 settes of the corpuscula, and sends a short, very delicate- 

 walled prolongation through the line of contact of the four 

 cells which are in process of dissolution, into each corpus- 

 culum which is to be impregnated (PI. LXV, figs. 3, 10). 

 In some cases the free cells contained in the pollen-tube 

 now appear to be much flattened, attached to the wall of 

 the tube, and divided into a larger number, normally six- 

 teen, of small cells lying in one plane (PI. LXV, fig. 4) ; 

 in other cases the pollen -tube contains four middle-sized, 

 or eight smaller, roundish cells, without any firm mem- 

 brane (PI. LXIV, fig. 3), and which probably have arisen 

 from repeated division of one of the large originally spheri- 

 cal cells. The protruded portion of the pollen-tube breaks 

 through the compact membrane of the upper end of the 

 corpusculum, forming a fissure which is very visible in the 

 apical aspect of the latter. Even after impregnation, the 

 ends of the tubes if carefully extracted appear quite 

 closed (PI. LXV, fig. 10). In an object so delicate as the 

 membranes of these tubes, a small opening might easily be 

 overlooked. The following observation, however, is de- 

 cisive as to the non-existence of any such opening : the 

 contents of the corpuscula, especially of those of Juni- 

 jperus sabina and communis, when just impregnated, swell 

 up after imbibing water, and rupture the wall of the cor- 

 pusculum. If a longitudinal section of the endosperm of a 

 germinal vesicle which has just been impregnated, is 

 placed under the microscope, it will be seen that as the 

 contents of the corpusculum swell, the delicate-walled pro- 

 longation of the pollen-tube which reaches into the upper 

 end of the corpusculum is intersected and ultimately 

 ruptured, whereupon an active current begins to flow out 

 of the corpusculum into the pollen-tube. Frequently, but not 

 always, one of the round cells in the pollen-tube forces its way 

 into the prolongation which is sent out by the membrane 



