28 Lang, Morphology of the Stock of Isoetes lacustris. 



These facts are available in the case of Isoetes and the 

 study of this existing plant affords at least a chance of 

 further insight into the morphology of Stigmaria, On 

 this view the rhizophoric base of Isoetes appears to be the 

 most directly comparable structure in recent plants to the 

 basal root-bearing region of the Lepidophytinae and 

 should hold a prominent position in any discussion of the 

 morphology of this. 



The general view of the morphology of the stock of 

 Isoetes reached by this preliminary enquiry is briefly that 

 it consists of a shoot-region and a rhizophoric-region. 

 The origin of the rhizophore may perhaps stand in some 

 relation to the deep-seated secondary meristem at the 

 base of the shoot. Once initiated, however, the growing 

 region of the rhizophore behaves like a primary apex 

 which is congenitally sunken and enclosed. This apex 

 is extended as a line in two-lobed forms and in three or 

 four directions in three or four-lobed stocks. It gives rise 

 to roots in acropetal order, and these when mature stand 

 exogenously on the surface, which is exposed by the 

 split. On this general view (which allows for the con- 

 flicting facts emphasised in Von Mohl's and Hofmeister's 

 explanations respectively, and confirms Williamson's 

 comparison with the organisation of the Lepidodendreae) 

 some details of the stock of Isoetes may be fruitfully re- 

 investigated in later papers. 



