THE EMBRYO IN GYMNOSPERMS. 



437 



(fig. 334 2). When the fruit is ripe and dry, these carpels form hard, woody achenes 

 which rattle in their loose sockets like teeth in the jawbone of a skull. 



Our descriptions of the fruit and its various forms and modifications rcilate, so far, 

 solely to the Angiosperms. In the Gymnosperms, however, several essential difier- 

 ences are to be noted. The account of their methods of fertilization (pp. 418-420) 

 was left at that stage at which the male sexual cell had fused with the egg-cell. 

 The nucleus of the fertilized egg now moves down to the base (away from the 



I' J' 



Fig. 331. — Collective and Aggregate fruits. 

 • Collective fruit of Betel Pepper (Piper Betle). 2 Aggregate fruit of Sweet-sop (Anona squamosa) formed by fusion of the 

 carpels of a single flower, s Transverse section of the same. * Longitudinal section of the aggreg.ite fruit of the Sour-sop 

 (Ano7ia muricata) produced in the same way. (After Baillon.) 



micropyle) of the egg-cell and divides several times, each product of its division 

 becoming enveloped in protoplasm and ultimately in a cell- wall. In the Gnetaceae 

 which many Botanists regard as more nearly allied to the Angiosperms than either 

 of the other two families of Gymnosperms (Coniferae and Cycadacene), there arise 

 in this way from 2-8 daughter-nuclei around each of which protoplasm aggregates, 

 and a cell-membrane is formed (c/. fig. 315 ^ p. 415). Between each of these cells 

 there is no connection: each grows out into a tube which penetrates the wall of the 

 egg-cell and pushes its way down into the reserve-food (endosperm) below. From 

 the tip of the tube a small cell, the embryonal cell, is cut off and from this cell by 

 further division and growth an embryo is produced, which is nourished by the food- 

 material. Of the many embryos which are inaugurated, one only comes to maturity, 

 and is found in the ripe seed. 



