jr f> 



THE VEGETABLE CELL. 53 



ing one or more sharply circumscribed round granules (the nucle- 

 oli, Kernhorperchen) ; the large round bodies are called the nuclei 

 (zellen-hern) or cytoblasts. The nuclei are usually smaller at 

 their first appearance than they are afterwards, so that their 

 growth is unmistakable. The surface of perfect nuclei appears 

 smooth and clearly defined, but it cannot be decided with cer- 

 tainty whether we ought to distinguish an enveloping membrane 

 and contents distinct from this, or to ascribe the membranous as- 

 pect of the outer layer to a somewhat greater density ; the nucleoli 

 always appear solid at first ; they often become hollowed out into 

 vesicles subsequently. The substances both of the nucleus and 

 of the nucleolus are coloured yellow by iodine. 



Ohserv. OiDinions differ very much as to the mode in which the nucleus 

 is formed from the granular protoplasm. Schleiden was the firbfc to dis- 

 cover the import of the micleus and to trace its development. Accord- 

 ing to Ms views (" Grundzuge^'' 3 ed. i, 208) they originate by the formation 

 of large granules in the protoplasm (afterwards the nucleoli) and other 

 granules becoming heaped up around these, and the whole becoming 

 more or less blended together and united into the nucleus. According to 

 Nageh's views (^^ ZeltscIiTifi. f. wi$s, Bot. Ill, 100, Hay /Society's FuhUca- 

 tions,'' 1849, p. 166), the nucleus is not formed by the union of a consider- 

 able mass at once, but appears first as a very minute structure, for tlio 

 rudiments of the nuclear body may be distinguished while they are yet 

 little larger than the globules of the protoplasm. He also assumes that 

 the nucleolus is formed firsfc, and then a layer of protoplasm is deposited 

 around it, which again becomes enclosed in a gelatinous membrane not 

 coloured by iodine ; JEofmeister {^^JSntwich d. Pollens,^' in ^^JBot. ZeiZ^ 1848. 

 "Die Mnstehung des Embryo,'' 1849, ^2) declares distinctly against both 

 these opinions. According to Ms researches, the formation of the nucleus 

 is not preceded* by the origin of nucleoli, but the nucleus presents itself 

 first under the form of a globular drop of a mucilaginous fluid, wMch be- 

 comes coated by a membrane over its outer surface. In many cases no 

 trace of a nucleolus can be seen in the nucleus at first, and one or more 

 (up to twenty) are subsequently formed in it, while hi other cases one 

 or more granules of a more solid substance swim in the fluid of the nucleus 

 from the very first, but not all of these are necessarily developed into 

 nucleoli, for only some of them can increase considerably in size and ac- 

 quire a membranous coat, the others becoming dissolved. Leaving out of 

 the question the membrane of the nucleus and of the nucleoli, the exist- 

 ence of wMch I never could satisfy myself, this latter view appears to me 

 the more correct ; that of ISTageli decidedly wrong. 



The second mode of origin of a nucleus, by division of a nucleus 

 already existing in the parent-cell, seems to be much rarer than 

 the new production of them, for as yet it has been observed only 

 in few cases, in the parent-cells of the spores of Anthoceros, in the 

 formation of the stomates, in the hairs of the filaments of Tra- 

 descantia, &a, by myself, Nageli, and Hofmeister ; but it is pos- 

 sible that this process prevails very widely, since, as the preceding 

 statements shew, we know very little yet respecting the origin of 



