Vol. 3] Torrey. — Biological Studies on Corymorpha. 289 



which have lost their original connection Avith the mesogloea, 

 massed within the circlet of canals and increased enormously in 

 bulk by the absorption of water. It is the formation of this 

 tissue that is probably chiefly responsible for the accelerated 

 growth of the stem from the time the axis begins to appear. The 

 canals increase in number and diameter as the stem enlarges and 

 exhibit an internal pressure which prevents their collapse. Yet 

 the great factor in the enlargement seems to be the growth of the 

 axial parenchyma by an increase both in the number and size of 

 its cells. 



Observing the loss of importance of the canals as they are 

 forced away from the center of the stem, it would seem natural 



Fig. 33. Portion of transverse section of adult of moderate size, 

 solnewhat contracted, showing relation of axial parenchyma to the epi- 

 thelium of the canals. X 88. 



to speak of the axial endoderm as encroaching upon and par- 

 tially obliterating the original cavity of the stem. Strictly 

 speaking, however, very little if any of the original cavity is 

 obliterated at any time by the axial tissue. On the contrary, 

 the original cavity, divided into several parts, has increased 

 greatly in total cross section, and the axial tissue, instead of 

 encroaching upon it, must be looked upon as a new growth 

 which has affected its form but without which the stem would 

 not have attained its present characteristic size. 



There is a certain relation between the number of canals, their 

 diameter and the diameter of the stem. Canals do not appear 



