546 MICROSCOPIC FORMS OF VEGETABLE LIFE THALLOPHYTE8 



smaller, it will be found, after the lapse of a few hours, that most of 

 them have subsided to the bottom ; in the course of the day they 

 will all be observed to be upon the point of subdivision ; on the 

 following morning the divisional brood will have become quite free ; 

 and on the next the bottom of the vessel will be found covered with 

 a new brood of dividing cells, which again proceed to the forma- 

 tion of a new brood, and so on. The activity of motion and the 

 activity of multiplication seem to stand, in some degree, in a relation 

 of reciprocity to each other ; for the dividing process takes place 

 with greater rapidity in the ' still ' cells than it does in the ' motile.' 

 What are the precise conditions which determine the transition 

 between the i still ' and the i motile ' states cannot yet be precisely 

 defined, but the influences of certain agencies can be predicted with 

 tolerable certainty. Thus it is only necessary to pour the water 

 containing these organisms from a smaller and deeper into a larger 

 and shallower vessel in order at once to determine segmentation in 

 numerous cells a phenomenon which is observable also in many other 

 protophytes. The ' motile ' cells seem to be favourably affected by 

 light, for they collect themselves at the surface of the water and at 

 the edges of the vessel, but when they are about to undergo segmen- 

 tation or to pass into the ' still ' condition, they sink to the bottom 

 of the vessel, or retreat to that part of it in which they are least 

 subjected to light. When kept in the dark the ' motile ' cells undergo 

 a great diminution of their chlorophyll, which becomes very pale, 

 and is diffused, instead of forming definite granules ; they continue 

 their movement, however, uninterruptedly without either sinking 

 to the bottom, or passing into the 'still ' form, or undergoing seg- 

 mentation. A moderate warmth, particularly that of the vernal sun, 

 is favourable to the development of the ' motile ' cells ; but a tempe- 

 rature of excessive elevation prevents it. Rapid evaporation of the 

 water in which the ' motile ' forms may be contained kills them at 

 once ; but a more gradual loss, such as takes place in deep glasses, 

 causes them merely to pass into the ' still ' form ; and in this condi- 

 tion especially when they have assumed a red hue they may be 

 completely dried up, and may remain in a state of dormant vitality 

 for many years. It is in this state that they are wafted about in 

 atmospheric currents, and that, being brought down by rain into 

 pools, cisterns, &c., they may present themselves where none had 

 been previously known to exist ; and there under favourable circum- 

 stances they may undergo a very rapid multiplication, and may 

 maintain themselves until the water is dried up, or some other 

 change occurs which is incompatible with the continuance of their 

 vital activity. They then very commonly become red throughout, 

 the red colouring substance extending itself from the centre towards 

 the circumference, and assuming an appearance like that of oil- 

 drops ; and these red cells, acquiring thick cell-walls and a mucous 

 envelope, float in flocculent aggregations on the surface of the water. 

 This state seems to correspond with the ' resting-spores ' of other 

 protophytes ; and it may continue until warmth, air, and moisture 

 cause the development of the red cells into the ordinary ' still ' cells, 

 green matter being gradually produced, until the red substance forms 



