5h ANATOMY AND PHYSIOLOGY OF 



nuclei. Nageli thinks tliat tlie process is similar to tliat in cell-divi- 

 feion, the membrane of the nnclens forming a partition, and the 

 two portions separating in the form of two distinct cells. I was 

 quite as unable to see such a membranous septum and a mem- 

 brane on nuclei generally, and the division appeared to me to take 

 place by gradual constriction. According to Hofineister's descrip- 

 tion (" Enstehung des Embryo/' 7) the membrane of the nucleus 

 dissolves, but its substance remains in the midst of the cell ; a 

 mass of gi'-anular mucilage accumulates around it ; this parfcs, 

 without being invested" by a membrane, into two masses, and 

 these afterwards become clothed with membranes and appear as 

 two secondary nuclei (toGhter-herne), 



It is still an unsolved question how often the process of divi- 

 sion of the nuclei can be repeated, whether it continue'^ indefi- 

 nitely, or whether after one or more divisions it becomes extinct, and 

 the formation of a new nucleus becomes necessary. In the spores 

 of Anthoeeros I found a second division, for in the parent-cell of 

 these a mass was formed, which first parted into two subdivisions, 

 and then each of these divided into two nuclei. Wimmel found the 

 same in the development of pollen-grains (" Zur EnUvhchelungs- 

 gesch d, Pollensf' — Bot Zeit, 1850, 22o). In these cases, there- 

 fore, a twofold division occurred. But, according to Wimmel, 

 the case is different in the formation of the parent-cell itself, for 

 when one of these cells is about to divide, a new nucleus is formed 

 in it, which becomes divided and gives rise to the development of 

 two secondary cells. When one of these secondary cells is to be 

 divided again, its nucleus takes no part in it but becomes absorbed, 

 a new nucleus being formed which divides, &c., so that here each 

 nucleus is capable only of one division. 



The number of nuclei that are formed in a cell varies very 

 much ; in most cases there are two, as in the formation of paren- 

 chymatous cells in the bark and the pith, in the formation of 

 vfood-cells in the cambium ; but in elongated cells, particularly 

 in hairs which become articulated, half a dozen or more nuclei are 

 often found lying in a row. In like manner varies the proportion 

 of the size of the nucleus to the cavity of the cell j in the paren- 

 diymatous cells of wood, in the cells of bark, and of the suberous 

 layer of the Dicotyledons, I found the micleus relatively very 

 small ; but in the hairs, in the cells of very small organs still con- 

 tained within the bud, as in the young leaves, in the cells of the 

 apex of the root, in which organs the cells divide while they 

 aie still very small, the nuclei occupy a very considerable portion 

 of the cavity of the cell. 



The formation of nuclei is soon followed by that of septa be- 

 tween eyery two of the former, which is effected by the primor- 

 dial utricle becoming folded inwards m the same manner as de- 

 scribed above of Conferva glomeTuta, till a partition is formed 

 reaching to the centre of the cell, and hy the deposition of cellulose 



