STRUCTURE OF THE BOLL 63 



coats, it reaches the tissues inside, and burrows through 

 them till the end reaches into the large central cell already 

 mentioned (Fig. 11, A, h) as containing the egg-cell and 

 its seven attendants. There the end of the tube literally 

 swells up and bursts, setting free the male nuclei inside 

 the large central cell, or, as it is commonly called, the 

 embryo -sac. One of the male nuclei fuses with the egg- 

 cell, as already mentioned, forming the unicellular Embryo. 

 The other fuses with two of the attendant nuclei, forming 

 a " triple-fusion nucleus," the fate of which is to provide 

 by its division some tissue called the " endosperm " 

 (Fig. 11, A, k), which at first surrounds the young 

 embryo, and is subsequently destroyed and digested by 

 it during its growth, until only a papery layer is left in 

 the ripe seed between the embryo and the seed-coat, 

 along with an outer papery Jayer which represents the 

 remains of the tissue in which the embryo-sac was 

 situated. Thus the embryo sac filled with endosperm 

 absorbs and digests the surrounding tissue up to the 

 seed-coats, and is itself absorbed and digested later by 

 the embryo, till only the embryo and certain layers of the 

 seed-coat are left alive, one complicated structure after 

 another having been in its turn developed and sacrificed 

 to its purpose. Lastly the seed-coat dies also. 



Of the many pollen-tubes which germinate on the style, 

 only some twenty or so can find an ovule. Those which were 

 too late in starting, or too slow in growing down the style, 

 also perish, and their remains may partly be traced in the 

 walls of the young fruits ; while the rest are thrown off when 

 the style breaks away from the point of the young boll. 



Some remarkable features of this race between the pollen- 



