PROTOPLASM 415 



Cucurbita, for instance, being more emulsoid than that of the 

 cells of Elodea. Protoplasm also exists in a state of gel which is 

 regarded as an active state capable of performing the functions 

 of growth and nutrition. The change from hydrogel to hydro- 

 sol, probably by the adsorption or imbibition of water, was 

 followed in the germination of spores of Mucor. The contents 

 of a freshly mounted spore are homogeneous and show no 

 protoplasmic movements. Water is absorbed, the spore swells, 

 and then the protoplasm, in the gel condition, forms a peri- 

 pheral layer. The contents become more opaque and the 

 structure becomes increasingly that of a hydrogel. Just before 

 germination the protoplasm passes into the hydrosol condition, 

 its small particles showing rapid oscillations. The growth 

 of the germ tube is at first rapid and into it passes most of 

 the protoplasm which occupies less and less of the total volume 

 as the hypha increases in size. In the hypha protoplasmic 

 plugs are formed by the aggregation of large motionless par- 

 ticles, their colloidal condition being considered to be in a 

 reversible condition intermediate between the states of sol 

 and gel. 



From the ultramicroscopic study of plasmolysed cells 

 evidence is obtained of the presence of a delicate membrane, 

 much finer in texture than that of the general protoplasm, 

 surrounding the protoplast and also occurring on the inner 

 side separating the central vacuole, when present, from the 

 cytoplasm. This plasma membrane also has been demon- 

 strated by the methods of micro-dissections. Experiments on 

 many and various organisms — Protozoa, Myxomycetes, Chloro- 

 phyceae, moulds, pollen tubes, oospheres of Fuciis, eggs of 

 echinoderms, etc. — indicate that all protoplasm is limited by 

 a membrane essentially protoplasmic in nature although dif- 

 fering in its physical properties, and possibly also in its chemical 

 constitution, from the general cytoplasm. This plasma- 

 membrane is a very thin, about o-i ju., elastic, and highly 

 viscous gel which can readily revert to the hydrosol condition. 

 If rapidly torn, disintegration of the whole membrane takes 

 place ; but if slowly torn, regeneration takes place and the 

 integrity of the protoplast is maintained. 



