Manchester Memoirs, Vol. lix. (191 5), No. 3. 21 



e. The difference in the cortical growth in relation to 

 the rhizophoric growing line from that outside the 

 secondary meristem in other regions of the plant. 



f. The correspondence between the growth of the 

 rhizophoric region of the stele and in the relation of the 

 roots and root-traces to it on the one hand, and the 

 growth of the stem stele and the relation of the leaves 

 and leaf-traces to it on the other. 



The divergence of opinion as to the morphology of 

 the stock of Isoetes and the imperfect treatment in the 

 text-books indicate that the problem is not a simple one. 

 The arrangement of the roots can be described from either 

 of the alternative points of view and both recognise that, 

 in the way its roots are borne, Isoetes is peculiar among 

 existing Pteridophyta. In seeking for the explanation 

 which best fits with all the facts of structure and develop- 

 ment it is important to avoid pre-conceptions. It is 

 indeed possible that both the interpretations suggested 

 may be in a measure correct and that the downward 

 growth may be associated in its origin with the peculiar 

 meristematic growth, but, once initiated, may behave like 

 a primary growing point in the production of lateral 

 members. In spite of the difficulties that have been 

 mentioned above, the recognition of the lower region of 

 the stock of Isoetes as a rhizophore in some way correlative 

 with the upwardly growing shoot appears to be justified. 

 This interpretation may now be tested by seeing how it(i) 

 gives a connected explanation of a number of peculiarities 

 in the growth and construction of the 'individual plant 

 and (2) facilitates morphological comparison with other 

 plants that are probably more or less directly related. 



In considering the explanation of the growth and 

 structure of the Isoetes stock itself it must be remembered 

 that the peculiarity of its growth is conditioned by the 



