THE EMBRYO IN GYMNOSPERMS. 



437 



(fig. 334 -). 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 relate, so far, 

 solely to the Angiosperms. In the Gymnospervis, 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 eea'-cell. 

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



^■r-r 



Fig. 331.— Collective and Aggregate fruits. 



1 CoUectiTC truit of Betel Pepper {Piper Betle). » Aggregate fruit of Sweet-sop (Anona squamosa) formed by fusion of the 

 carpels of a single flower. 3 Transverse section of the same. * Longitudinal section of the aggregate fruit of the Sour-sop 

 (^AnoTia 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 

 wliich many Botanists regard as more nearly allied to the Augiosj^erms than either 

 of the other two families of Gymuosperms (Coniferee and Cycadaceaj), 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. 



