192 



CASSELL'S POPULAE GAEDENIlfG. 



In this embryo-sac are suspended three masses of^ 

 protoplasm (not shown in the woodcut), each with a 

 nucleus. One of these three is destined to become 

 the egg, and may be called the germ, or " oosphere ;" 



for work when stimulated by the arrival of the pollen- 

 tube and its contents. 



The poUen-tube travels down the style, as we have 

 seen, worms its way along the stalk of the ovule, 

 enters the microprle, already referred to (Fiors. 86, 

 87), and comes into contact \\-ith the ombryo-sac. 



Formation of the Oospore, or Egg. — 



Then happens a remarkable series of changes, 

 eventuating in the formation of the egg, as we may 

 call it, and the embryo plant den^'ed from it. The 

 changes in question, so far as known, may briefly be 

 described as the passage of the end of the pollen- 

 tube, with its nucleus and protoplasmic contents, 

 into one of the " synergides '" — in other words, the 

 protoplasm of the pollen-tube and that of the synergid 



Fig. 85. — FertilisatiOD of the Oviile, showing the passage of 

 the FoUen-tubes from the Stigma to the Orules. 



Fig. 86. — An Ovule with 

 Pollen-tube entering the 

 Micropyle (ma^uifiedj. 



i ig.bT. — Section of Ovule 

 of Polygonum (en- 

 liirged), showing the 

 two coats or sheaths, 

 the Micropjle, and 

 a Pollen-tube peue- 

 tratiug the Enibr/o- 

 sac. 



the other two are called " synergides," a word for 

 which no English equivalent has yet been found. 

 Their use will be mentioned later on. At the other 

 end of the embryo-sac are three minute cells, each 

 with a nucleus ; these are the " antipodal cells," 

 which in this place we may dismiss with the mere 

 mention, as their relation to practical matters is only 

 remote. The contents of the embryo-sac (other than 

 the oosphere) are supposed to correspond to a pro- 

 thallus, such as exists in some Cryptogams. The 

 nucellus of the ovule, with its embryo-sac, containing 

 oosphere, synergides, and antipodal cells, is equipped 



mix, and the nucleus of both disappears, the one 

 entirely, while the other is temporarily disintegrated. 

 The synergid now has a uniformly granular com- 

 position, and an irregularly lohed form. One or 

 more of these lobes come into contact with the germ, 

 or oosphere, which, like the synergid, has up to this 

 time been a -mere mass of protoplasm enclosing 

 a nucleus ; but the oosphere now, after contact and 

 fusion with the synergid, develops a cell-wall, and a 

 second nucleus becomes apparent. This second 

 nucleus is supposed to be derived originally from 

 the pollen-tube, to be broken up, or diffused, as 



