Manchester Memoirs, Vol. lix. (191 5), No. #. 19 



tion of the increase in depth of cortex found in the 

 apical growth of all ordinary roots and shoots. In Iso'etes, 

 however, the process continues throughout life in relation 

 to the very slight growth in length of the stock. What is 

 undoubtedly cortical extension is seen in young plants of 

 Iso'etes before a secondary meristem is established. Two 

 other pieces of evidence from the older plants in support 

 of this alternative explanation of the cortical growth may 

 be noted. They are (1) the fact that the older leaf- and 

 root-traces are stretched throughout their whole length 

 and not only at the level of the cambium, and (2) the fact 

 that cortical extension continues as usual in stocks where 

 there is practically no secondary growth and in which a 

 secondary meristem is only developed at the base of the 

 stem stele. 



The main facts as to the construction of the stock of 

 Iso'etes have been reviewed in the preceding paragraphs 

 and may now be considered in their bearing on the mor- 

 phology of the stock. Two alternative interpretations 

 of this, especially as regards the nature of the lower root- 

 bearing region, were evident from the survey of the work 

 of previous investigators. 



The following features may be regarded as supporting 

 the view that the root-bearing region is a result of the 

 peculiar secondary growth of the stem and is not to be 

 regarded as a " caudex descendens" or rhizophore cor- 

 relative with the upwardly growing shoot : — 



(a) The coincidence of the deeply-seated growing 

 line of the rhizophoric region with the meristem around 

 the base of the stem stele. 



(b) The frequent extension upwards of the horns of 

 the rhizophoric portion of the central vascular axis, at the 

 expense of the adjacent secondary meristem of the shoot. 



(c) The appearance of an arrangement of the roots in 



