270 The Sex and Generative Organs of Plants. 



no doubt regarding it. According, however, to one observer, 

 Schleiden, this process takes place somewhat differently : 

 for he says, that when it has arrived at the embryo sac, 

 thS pollen tube sinks down in it, pushes it before it, and be- 

 comes imbedded in it. When the pollen tube has once come 

 to lie in the sac, and when it has swelled out at its further 

 end like a ball or an egg, it is supposed itself to become 

 the new embryo. Regarding this last point, various opi- 

 nions prevail among physiologists, and most of them have 

 not expressed themselves decidedly on the fubject. But 

 supposing Schleiden right, yet so much remains certain, 

 that from the peculiar action of the pollen tube on the 

 cell destined for its reception, it is converted into a seed, in 

 as much as from the organisable contents of the pollen tube 

 and embroyo sac, cellular tissue is gradually deposited and 

 becomes more and more firm. That part of the pollen tube, 

 which lies outside the embryo sac, or at some distance 

 from it, withers up completely, its separated end blends 

 with the embryo sac, or is absorbed and obliterated, and by 

 progressive depositions, the individual parts of the embryo 

 and its encircling albumen are formed. 



Those membranous envelopes which had grown round 

 the ovule from beneath upwards, get harder by degrees ; 

 this commonly happens in such a way, that the outer forms 

 the external, and the inner the internal, integument. 

 When these coverings close over the top of the ovum which 

 was originally open, and its internal cellular structure deve- 

 lopes itself, it becomes completed and is a seed. This process 

 takes place in the vegetable kingdom with great variety, for 

 sometimes more, and sometimes fewer, than two integuments 

 of the skin are developed ; the ovule separates itself in 

 the greatest variety of ways, by consecutive layers of cellular 

 tissue raised above each other, and at last escapes from 

 the pistil, now become a fruit, and begins 'the life of a new 

 independent being. The foregoing are the most important 



