112 VEGETABLE CELLS. 



deduce a general law, and, in addition, to point out 

 some essential differences within the bounds of this law. 



The phenomena which accompany free cell-formation 

 may be seen with the greatest certainty in the origin of 

 the germ-cells of Zygnema, the sporangial cells of Achlya, 

 and the larger cells produced by abnormal formation in 

 Bryopsis, Conferva, and other Algse. Here a portion 

 (in Zygnema the whole) of the contents becomes isolated, 

 acquires a globular or ellipsoidal form, and produces a 

 perfect closed membrane all over its external surface. 

 In the prevalent opinion on free cell-formation, it has 

 been hitherto assumed that the membrane originates 

 around a nucleus. In the cases mentioned here there 

 cannot be any doubt that the membrane originates around 

 the contents. It was further assumed that the membrane 

 was formed first and the contents subsequently. Here, 

 however, the contents are decidedly primary and the 

 membrane secondary. 



The mode of origin of the endosperm-cells in the 

 embryo-sac comes next to these facts. Observation 

 shows here, first a nucleus, then a layer of mucilage which 

 surrounds this nucleus, lastly, a distinct membrane which 

 incloses the mucilage together with the nucleus. The 

 phenomena accessible to observation leave the place and 

 epoch at which the membrane originates undecided. The 

 assumption that it is formed immediately around the 

 nucleus is, therefore, still within the bounds of possi- 

 bility. But it would appear to me uncalled for and 

 superfluous, since no fact nor analogy are in its favour.* 

 If we assume, on the other hand, that a definite quantity 

 of mucilage collects around the nucleus, and that the cell- 

 membrane originates around this mucilage, the assump- 

 tion on the one hand fully meets the appearances in the 



* Schleiden's observations certainly are contradictory to my representa- 

 tion and interpretation, and these points are still open. Formerly I thought 

 that I also saw cell-formation round the nucleus. I have studied the pro- 

 cesses occurring in the embryo-sac repeatedly, for several years, and in 

 different plants ; with more accurate observation, however, I can no longer 

 find any condition which perfectly agrees with Schleiden's representations. 



