160 r. 0. BOWER. 



comes over the strings after plasmolysis, is due^ at least in a 

 great measure, to a drawing out of fresh substance from the 

 main protoplastic body, and a consequent thickening of the 

 individual strings, which at the same time become less tightly 

 stretched. It is not, however, asserted that lateral coalescence 

 of strings never occurs; it is only to be expected that in their 

 rapid vibratory movements strings should come into contact 

 with one another and remain coherent, but this has not been 

 directly observed. 



It has been stated that before reagents, which are liable to 

 injure living protoplasm, the strings alter their appearance, 

 become ropy and slack, and often break away. Similar 

 changes occur after plasmolysis has been continued for a long 

 time, and death supervenes in the plasmolysed cells (cf. 

 de Vries, I.e., p. 66, &c.). In dead cells the contracted proto- 

 plasm is completely isolated, or only connected with the walls 

 by a few ropy strings, which differ in general appearance from 

 those of living cells, and do not show the vibratory movements. 



When the strings break away their free ends often execute 

 irregular movements, while they contract gradually, as described 

 by Pringsheim and Gardiner, on the one hand to the proto- 

 plasm, on the other to the cell wall. 



It has already been noted by several observers in various 

 plants that the protoplasm does not always contract as a single 

 mass. This is sometimes the case in cells of the prothallus, 

 the protoplasm dividing into two (or more?) rounded portions; 

 Avhen this occurs the masses are usually seen to be connected 

 by strings of protoplasm of rather coarse texture ; these are, 

 doubtless, of a similar nature to those which connect the con- 

 tracted protoplasm with the cell wall. 



In conclusion, it may be noted that the walls separating 

 contiguous cells of the prothallus of the above species have 

 not a perfectly smooth surface, but show, after the protoplasm 

 has receded, slight inequalities in thickness when observed 

 with a high power. 



Such being the results obtained by the study of plasmolysis 

 of cells of prothalli of ferns, the next step was to see whether 



