58 ORGANOGRAPHY. 



important element in free cell-formation, indeed, if his view 

 of this formation be correct, it appears to me that it can only 

 be retjarded as a modification of the process of cell-division. 

 In Flowering Plants free cell- formation only occurs in the 

 embryo-sac, in which part both the germinal vesicles and the 

 cells of the albumen (endosperm) originate according to this 

 method. In the Flowerless Plants it is regarded by some ob- 

 servers, as the mode by which the spores of Lichens, and some 

 of the Algjc and Pungi, originate; by Henfrey and others, how- 

 ever, their formation is believed to be due to a modification of 

 the process of cell-division. 



2. Free Cell-formation without a previous nucleus. — In the pro- 

 cess of free cell-formation, as described above, we have alluded 

 to the production of the nucleus as the first step of the process, 

 and it is regarded as such in most instances by far the greater 

 number of observers. In some cases, however, no nucleus can 

 be detected in a cell previous to the formation of other cells 

 free in its cavity; hence it is quite clear that the presence of the 

 nucleus cannot always be regarded as essential, but that the 

 separation of a portion of protoplasm from the general mass, 

 which takes place under such circumstances, must be capable of 

 acting as one, and thus to cover itself with a membrane and 

 form a cell. This, according to Mohl, frequently occurs in the 

 formation of the spores of the Algte, &c. 



In the ordinary course of vegetation, free cell-formation can 

 only take place in the protoplasmic fluid contained in tlie in- 

 terior of cells forming ])arts of living tissues, although, accord- 

 ing to Schleiden, Mohl, and others, " it may also occur in- 

 dependently of the life of the parent plant in the creation of 

 parasitic Fungi, Yeast cells, &c., both in the decomposing fluid 

 of cells, and in the excreted or expressed juices." 



2. Cell-division. — This mode of cell- formation is also called 

 by authors parietal cell-formation, and merismatic or fissiparous. 

 It maybe treated of under two heads, namely : I. Cell- division 

 without ahsnrption of the jvalls of the parent cell, and 2. Cell- 

 division with absorption of the ivalls of the parent cell, arid the 

 setting free of the new cells. 



1. Cell-division loithout absorption of the walls of Oie parent 

 cell. — Tliis mode of cell formation was first discovered by ISIohl, 

 whose oi)inions were afterwards ably supported by Ilenfrcy 

 and Mitschcrlich. According to these physiologists, (and their 

 observations have now l)ecn confirmed in all essential parti- 

 culars by various subseciuent observers,) this process is the one 

 by whirh all ve;:ctating or growing i)arts of plants, whether 

 Flowering or Flowerless, are produced and increased ;— all 

 increase in the mass of the ditferent organs is therefore due to 

 its agency. The manner in which it takes place is as follows: — 

 The ]irin'iordial utricle or the protoplasmic lining of the cell, 



