238 CONTRIBUTIONS TO 



will, probably, on more accurate investigation, be mostly re- 

 duced to one of these substances. These substances, however, 

 soon become dissolved, and converted either into sugar or gum ; 

 both changes take place at times, even before the pollen-grain 

 has commenced to send forth tubes upon the stigma, frequently 

 during the gradual descent of the pollen -tube through the 

 style to the ovule ; so that in some cases unaltered starch may 

 still be found even in the embryonal extremity. 



At both these situations the before -mentioned minute 

 mucus -granules are very soon developed in the gum, upon 

 which the solution of gum, hitherto homogeneous, becomes 

 clouded, or when a larger quantity of granules is present, 

 more opaque. Single, larger, more sharply defined granules 

 next become apparent in the mass (fig. 2, the upper part) ; 

 and very soon afterwards the cytoblasts appear (fig. 2, the 

 lower part), looking like granulous coagulations around the 

 granules. The cytoblasts, however, grow considerably in this 

 free state ; and I have observed, in Fritillaria pyrenaica for 

 instance, a gradual expansion from 0'00084< to 0*001 Paris inch. 



So soon as the cytoblasts have attained their full size, a 

 delicate transparent vesicle rises upon their surface. This is 

 the young cell, which at first represents a very flat segment of 

 a sphere, the plane side of which is formed by the cytoblast, 

 and the convex side by the young cell, which is placed upon 

 it somewhat like a watch-glass upon a watch. In its natural 

 medium it is distinguished almost by this circumstance alone, 

 that the space between its convexity and the cytoblast is per- 

 fectly clear and transparent, and probably filled with a watery 

 fluid, and is bounded by the surrounding mucus - granules 

 which have been aggregated together at its first formation, 

 and are pressed back by its expansion, as I have endeavoured 

 to represent it in plate XV, figs. 4, 5, 6. But if these young 

 cells be isolated, the mucus-granules may be almost entirely 

 removed by shaking the stage. They cannot, however, be 

 observed for any length of time, for in a few minutes they 

 become completely dissolved in distilled water, leaving only 

 the cytoblasts behind. The vesicle gradually expands and be- 

 comes more consistent (fig. 1, b), and, with the exception of the 

 cytoblast, which always forms a portion of it, the wall now con- 

 sists of gelatine. The entire cell then increases beyond the 



