THE PLANT-CELL. 2? 



Flemming considers that isolated granules are never to be found in 

 nuclei : he regards the apparent granules as being the transverse sections 

 of the trabecular fibres. Strasburger is of opinion that the recticulum is 

 in reality a single convoluted fibre, consisting of protoplasm (nucleo- 

 plasma) in which microsomata are imbedded ; the nucleoli are large 

 microsomata. 



Chemically considered the nucleus appears to consist, 

 principally at least, of a substance termed nucletn, which is 

 allied to the proteids, but differing from them in that it 

 contains phosphorus but no sulphur. Miescher ascribes to it 

 the formula C n H*Nf) v 



Flemming finds that there is a substance present in the nucleolus 

 and in the frame-work which stains readily when treated with various 

 colouring-matters (haematoxylin, safranin, nigrosin) ; to this he gives the 

 name of chromatin, the substance which does not stain being termed 

 achromatin. These substances, or at any rate chromatin, may be bodies 

 of definite chemical constitution. 



According to Zacharias, the more solid parts of the nucleus consist of 

 plastin and of nuclem ; the nuclem he considers to be the chromatin of 

 Flemming. 



The fact that a nucleus has now been found in almost 

 all living cells seems to shew that the presence of such a 

 body is of importance to the life of the cell, but it is not yet 

 possible to ascribe to it any definite function. It is the 

 general rule that, in the process of cell-division, the division 

 of the nucleus precedes that of the protoplasm, and this, 

 together with the fact that the granules in the protoplasm 

 may frequently be seen to be arranged in lines radiating from 

 the nucleus, would seem to indicate that the nucleus, is the 

 centre of the molecular forces of the cell. Strasburger and 

 Schmitz have however come to the conclusion that the proto- 

 plasm is the active agent in cell-division, and that the division 

 of the nucleus is induced by that of the protoplasm. It has 

 been suggested that the nucleus is of importance in con- 

 nexion with the nutrition of the cell, a view which is sup- 

 ported by the fact that when cells attain a very great size 

 (e.g. Vaucheria-filaments, hyphae of Fungi, laticiferous cells) 

 they become multinucleate. Strasburger is of opinion that 

 it is especially connected with the formation of proteid-matter 

 in the cell (see Lecture IX.). 



