96 Randolph : Influence of moisture upon ivy 



ning of the experiment. These roots, like those above mentioned 

 that grow from holdfast-roots, have the same appearance as roots 



that grow from stems under water. 



If young stems with green holdfast-roots beginning to grow 

 out are kept in a vessel of water in saturated air, the growth of the 

 holdfast-roots that are above the water continues, but the part that 

 has grown in saturated air is white and covered with root-hairs. 



In one instance, occurring in some slips growing in a pot of 



damp sand in the greenhouse, roots appeared on the sides of the 



stems about two centimeters above the sand and grew out and 



' downward obliquely into it. They resembled the prop roots of 



Indian corn. 



Thus under varying conditions the English ivy has seven 



classes of roots : 



1. The roots of the seedling. 



2. Holdfast-roots by which it clings to walls. 



3. Roots arising from the stem under water. 



4. Roots arising from the stem in an atmosphere saturated 

 with water. 



5. Roots arising from holdfast-roots under water. 



6. Roots arising from holdfast-roots in an atmosphere satu- 

 rated with water. 



7 



air. 



I have not examined the structure of roots of class 1. 



In the other roots the same kinds of tissues are present, but 

 there are differences in the size or in the number of certain cells 

 that give a characteristic appearance to sections of the different 

 roots. 



The structure in general is as follows : The epidermis consists 

 of two (in one case of three) layers, with (or without) root-hairs \ 

 the cortical parenchyma is about five cell-rows in thickness ; the 

 endodermis surrounds the fibro-vascular bundles ; and in the cen- 

 ter there is a column of sclerenchymatous cells. Lying within 

 the endodermis, next to it and also next or very near to the outer 

 vessel of each bundle, are ducts lined by secreting cells. When 

 the roots increase in thickness the ducts continue to lie next to 

 the endodermis. 



