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238 CONTRIBUTIONS TO will, probably, on more accurate investigation, be mostly reduced 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 lke 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 perfectly 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 becomes more consistent (fig. 1, b), and, with the exception of the cytoblast, which always forms a portion of it, the wall now consists of gelatine. The entire cell then increases beyond the