AN ARTIFICIAL OSMOTIC CELL 55 



To sum up. Crowding affects the growth in the five follow- 

 ing ways: (1) By a diminution of the number of stems produced 

 by the average fragment of KMn04. (2) By a diminution of 

 the total length (the sum of the lengths) of the stems produced 

 by the average fragment. (3) By the appearance of very tall 

 specimens. (4) By the appearance of very short specmiens. 

 (5) By a larger deposit of KMn04 wdthin the surface-canals. 

 There is a sixth way, which does not appear from the tables. 

 The stems, with the exception of the very tall ones, are not as 

 clear-cut and regular where the crowding is beyond a certain 

 point. They are matted together; they cling to and twine around 

 each other. 



The circumstances which, when the growths are crowded, 

 result in the better development of a few at the expense of the 

 greater number, may be summed up briefly as follows: 



1. A situation of the fragment of KMn04 where a large area 

 of its surface comes in contact with the medium. As the osmotic 

 sac continually dehydrates the medium, and becomes surrounded 

 by a concentrated zone of the colloid solution, the higher it is 

 situated above the bottom of the vessel, the better will be the 

 growth. For the concentrated solution around the osmotic 

 sac being of a higher specific gravity, continually falls downward 

 and, is replaced by a solution containing a larger amount of water 

 upon which the osmotic sac draws for its supply. 



2. A situation of the fragment near the wall of the vessel. 

 As has been remarked, the apposition of the stem against a 

 foreign body makes for economy of substance, and the less 

 substance is required to form it, the faster will it grow. Owing 

 to the fact that the stem grows towards the warmest point, the 

 shape of the vessel and the material of which it is made will 

 have a bearing in bringing a stem to or away from the vessel- 

 wall. When a stem is situated on the cooler side of a circular 

 vessel, made of a poor heat conductor, such as glass, it will 

 move toward the center of the vessel,, where the heat-rays are 

 focussed. When a stem is situated, on the other hand, near 

 the warmer side of the vessel, it will approach the wall, cling 

 to it, and proceed to grow at an advantage. 



