OF HETEROGENESIS 215 



growth of plants of Vallisneria in West Middlesex water and in 

 the New River water respectively. They have always seemed to 

 grow much more rapidly and vigorously in the latter than in the 

 former, a fact doubtless due to some differences in the saline 

 constituents of the waters, and the greater abundance of lime salts 

 in that from the New River. When tap water has been mentioned 

 hitherto it has always been West Middlesex water that has been 

 referred to. I wished, however, to ascertain what would be the 

 result of keeping Nitella for a time in New River water, and 

 accordingly, towards the end of 1898, I made the following 

 experiments and observations. 



Fresh specimens of N. flexilis were kept for four or five weeks 

 in an open vase on the mantelpiece containing this New River 

 water, and portions were cut off, from time to time, and placed 

 in small covered, earthenware pots containing distilled water only, 

 and allowed to remain there for a variable number of days. 



On several occasions, after only three or four days of this change 

 of conditions, I have found many of the previously healthy 

 cells completely altered, and that often in two different ways in 

 contiguous cells. In each case, however, the cells had com- 

 pletely lost their bright green tint and had assumed either a 

 spotted appearance or a more uniform drab or earthy colour, as 

 shown in Fig. 36, B (x 25). 



Two of the cells there represented, which showed the uniform 

 drab or earthy colour, were found to be crammed from end to end 

 with a continuous layer of minute motionless Amoebae, which 

 had completely replaced the layer of chlorophyll corpuscles. 

 This extraordinary result is shown in Fig. 37, B (x 375), as it 

 occurred in a terminal axis cell, which was in a healthy condition 

 when placed in the pot three days previously. Many of these 

 minute Amoebae contained brownish or olive-coloured residual 

 granules. Between them a few motionless Bacteria were to be 

 seen here and there ; but not a single green chlorophyll corpuscle 

 was left. 



This particular change has not been confined to specimens of 

 N. flexilis treated in the manner above stated. I had not unfre- 

 quently met with it before I began to make use of the New River 

 water, as my notes show, and always in association with the 

 common change — that is, the two changes often occurred in 

 contiguous cells in the most puzzling manner. I can find no 

 details as to the conditions under which this particular change was 



