1 88 NATURAL SCIENCE. Sept.. 



which He the very foundations of botanical science. In his earUest 

 contributions (29) he ascribes to the nucleolus a two-fold structure ; 

 it consists, he says, of comparatively dense and resistant plastin, and 

 of more easily soluble proteids. Plastin, it may be remarked here, is 

 the characteristic proteid of the protoplasm, of which it forms the 

 framework, and Zacharias has been led by his observations to con- 

 clude that it is likewise the framework of the nucleus and its parts ; 

 hence, instead of employing the special term " linin " for the nuclear 

 threadwork, as is done by many other authors, he uses " plastin " to 

 denote the formed constituent both of the protoplasm and of the 

 nucleus. 



Carnoy has also come to the conclusion that the nucleolus 

 consists of dense plastin and of less dense proteid substances, but of 

 no nuclein. In 1885 Zacharias issued his article on the " Nucleolus" 

 (30). He examined particularly the case of Galanthns nivalis (Snow- 

 drop), because here he was able to obtain large and favourable 

 examples. These observations fully bore out his former views, and 

 he further was brought to the belief that the plastin may be con- 

 sidered as arranged in a network, with the other proteids occupying 

 its meshes. But of this he makes no positive statement, waiting for 

 others to confirm these points. 



In the last-mentioned article we find the behaviour of the 



nucleolus towards various solvents and staining reagents very fully 



discussed. With pure water, it seems, the nucleolus is unchanged, 



while the other nuclear parts, including the chromatic portions, swell 



up and become transparent, thus rendering the nucleolus particularly 



evident. As the water is further imbibed into the nucleus, this 



increases in size, and finally bursts, liberating the nucleolus as a 



shining, sharply defined body. Alcohol also brings out the nucleolus 



clearly. Prolonged action of 10 per cent, sodium chloride solution 



extracts from the nucleolus a portion of its substance, and leaves 



behind a part which has a loose constitution and slight power of 



staining. A somewhat similar removal of a portion of the nucleolar 



substance is brought about by the penetration of artificial digestive 



fluids. These render the nucleolus indistinct, and cause a diminution 



in its size ; the remnant which is left behind no longer stains with 



neutral carmine solution, and a 10 per cent, common salt solution has 



no action upon it. The digestive fluid leaves the nuclein-grains 



unaffected, and it can be seen that, abundant as these may be in and 



around the nuclear threadwork, they are entirely absent both from the 



nucleolus and the protoplasm. The action of common salt and of 



digestive fluids upon the nucleolus gives great probability to the view 



that this structure consists, as Zacharias and Carnoy affirm, of two 



separate materials, and is not built of a single substance (pyrenin) as 



Schwartz and others maintain. 



The action of carmine stains also sheds considerable light upon 

 the constitution of the nucleolus. Neutral carmine colours that part 



