PROGRESS IN CYTOLOGY 175 



" endoplasm." Pfeffer extended this idea by stating 

 that all exposed protoplasmic surfaces were covered by 

 " plasmatic membranes " of different composition from 

 the rest of the living substance. 



The contents of the different segments of a sieve tube 

 had been shown by Hanstein in 1864 to be in continuity 

 with each other through perforations in the sieve plate, 

 and this had been confirmed by Russow and Strasburger 

 in 1882, while protoplasmic continuity between the cells 

 of certain Algae had also been demonstrated by several 

 investigators. In 1897 Gardiner, by the use of improved 

 methods, was able to show that protoplasmic inter- 

 communication was a characteristic of all living cells. 



By 1880 the universal presence of a nucleus, discovered 

 by Robert Brown fifty years before, had been accepted 

 as a fact, and its importance in cell-division had come to 

 be recognised, but its structure and functions were as yet 

 very imperfectly known. Strasburger and Flemming 

 were the first to study it in detail and to show that it 

 consisted of a homogeneous or finely granular matrix 

 in which lay imbedded a reticulum or greatly coiled fibre. 

 One granule much larger than the rest received the name 

 of nucleolus. The reticulum itself consisted of a non- 

 stainable basis called achromatin or linin, with imbedded 

 granules of chromatin. The nucleus as a whole was 

 also seen to be enclosed within a nuclear membrane. 

 Chemically the nucleus was composed essentially of a 

 compound rich in phosphorus known as nuclein, and this 

 again was analysable into albumin and nucleinic acid. 

 Flemming and Van Beneden had demonstrated the 

 occurrence of an accessory body, the centrosome, in 

 animal cells, but, in spite of Guignard's attempts to prove 

 its existence in Phanerogams, plant nuclei, save those of 

 Hepaticae, in which Farmer proved their presence, and, 

 according to Williams, Mottier and others, those of 

 Algae, appeared not to possess such bodies. 



At the same time great progress was made in un- 



