MICRODISSECTION 241 



a system shall be a sol or gel. Hence viscosity measurements in 

 themselves are not sufficient. 



Seifriz regarded cytoplasm as being formed of either an en- 

 tangled mass of fibres or as an orderly arrangement of chains of 

 molecules ; the fibrous ground substance being protein in nature. 

 Heilbrunn has disagreed with this view, and thinks it to be a 

 suspensoid in nature. 



Chloroplast. The nature of the chloroplast in Spirogyra has 

 been investigated by Scarth with microdissection methods. 

 According to this investigator it is usually an elastic jelly of 

 doughy consistencey. When pushed about or stretched with the 

 needle it preserves its irregularity of outline and sometimes breaks 

 across. It is sufficiently plastic to be pushed through an opening 

 narrower than its own diameter. 



Nucleus. Chambers has described the metazoan nucleus as 

 being fluid in nature and showing no visible structure, with the 

 exception of one or more nucleoli and the nuclear membrane. It 

 is quite otherwise with the nuclei of plants. They range from 

 apparent homogeneity (Symphoriocarpus and Spirogyra) through 

 fine-grained heterogeneity {Elodea) to a coarsely mottled appear- 

 ance (Tradescantia). When the cytoplasm is stripped from the 

 nucleus of Spirogyra it takes the form of a smooth, transparent 

 sphere. If it be punctured, the contents are ejected violently. 

 The liquid portion is quickly dispersed and the solid portion then 

 becomes visible. In Tradescantia the solid portion, when extruded, 

 shows an irregular folded mass corresponding to the more highly 

 refractive portion of the normal nucleus. This gelatinous portion 

 is sufficiently plastic to be deformed as it passes through an opening 

 and it sets to a tough elastic jelly outside. In Elodea the fine- 

 grained nucleus ejects its contents as small irregular lumps of 

 jelly. In Symphoriocarpus, although the nucleus appears to be 

 homogeneous, on ejection, the contents show as a small portion or 

 flock of coagulum. The nuclear membrane disappears immediately 

 the nucleus is injured. 



There is a conflict of evidence w4th regard to the origin of the 

 nuclear membrane. It has been considered by some as being 

 of cytoplasmic origin. According to Scarth two membranes are 



