31 



1. Because "by this forra greater varieties of soil can be readied. 



2. Because siich forras pass raore easily around obstacles. 

 The mechanical functions are as holdfasts and for purposes of 

 absorption. The reason for general downward direction is undoubted- 

 ly force of gravity. This geotropism may be the result of heredity. 

 Originally the roots may have assumed this position in its search 



for food and the habit may feave become fixed. Exceptions are common. 



as aerial roots in ivy ; water hyacinth, etc. 



Cypress knees, supposed to be the resiilt of growing in stagnant water 



for piirposes of aeration. Here another force works against 



geotropism. 



study Q , f Leucobrym . 

 Cells coniiected by pores. Three layers, with chlor, in the 

 central one. Air cells on surface guarding chlor. cells within. 

 If placed in water, epidermis becomes transpareait and leaves appear 

 green. Can be grown for several years withoiit developing rhiaoids-. 

 Leaves absorb water as in Sphagnum. 



Prof. Barnes of Chicago University believes that mosses absorb 

 water entirely through leaves, not at all through stems. Dr. 

 Cowles believes condixction throiigh leaves more important than through 

 stem but not entirely the way. Ilosses if placed in water become 

 wet immediately, showing the absorption. Lichens absorb water 

 eagerly. Probably take in also some mineral food from the substratum 



since they decay rocks. 



Asclepias incarnata growing in the water showed roots containing 

 chlor. 



J 



