MICRODISSECTION 239 



MICRODISSECTION 



Thanks to the investigations of Chambers and his co-workers, 

 a very considerable amount of information is now forthcoming 

 regarding the nature of the nucleus and cytoplasm in the living 

 cells of animals. Unfortunately at present our information is 

 comparatively meagre with regard to plant tissues. The principal 

 barrier that has reacted against noteworthy advances in the 

 microdissection of plant cells is the presence of a resistant cellulose 

 wall. The delicate glass needle used in these investigations is 

 unable to pierce the plant wall and becomes broken. It is thus 

 a purely mechanical difficulty which stands in the way of any 

 advance in this field of plant cytology. 



Nevertheless, in spite of these obstacles, a start has now been 

 made in this branch of the subject, and the more outstanding 

 investigations will be considered here. 



Cytoplasm. Scarth has investigated the nature of the cyto- 

 plasm in the living cells of the mesocarp of the Snov/berry, 

 Symphoriocarpus. It was found that the strands of cytoplasm 

 were frequently rigidly inextensible, so that when they were 

 slightly stretched they often broke across and recoiled back like 

 a snapped thread. At other times the threads appeared as gushing 

 streams. In this streaming condition, they appeared to be viscid 

 and highly extensible and could be pulled into threads less than a 

 micron in diameter. A needle pushed through a rapidly moving 

 cytoplasmic strand in the staminal hairs of Tradescantia, for 

 example, carried the viscid cytoplasm like a film over the point of 

 the needle as it emerged on the opposite side of the hair. When 

 the needle was moved backwards and forwards in the axis of a 

 strand, the respective portions of the latter lengthened and 

 shortened elastically, with little or no slipping of the needle. 

 Streaming is therefore comparable, not only with high viscosity, 

 but also with definite elasticity. Again, in Spirogyra the nucleus 

 may be pushed from end to end of the cell, and it immediately 

 recoils to its original position when released. 



The question of the viscosity of cytoplasm has been a matter of 

 controversy. It is generally recognised at the present time that 

 protoplasm represents a complex colloidal system. Chambers and 



