Manchester Monoirs, Vol. hi. (19 12), N'o. Vi. 13 



intrusive and the internal endodermis not a tissue 

 boundary between the stele and an intrusive cortex. It 

 will be clear that this view fits with the progressive 

 development of the stele of Heliniutliostac/rys and is con- 

 sistent with the comparisons made between this plant and 

 the Coenopterideae. As regards BotrycJiiiun lunarta the 

 study of a number of plants cut in complete transverse 

 series from base to apex has shown considerable variety 

 in the development of an internal endodermis. There 

 may be no internal endodermis extending into the stele 

 throughout the whole development, while in other cases in 

 which appearances consistent with an explanation of 

 " pocketing" or " intrusion " are found at the lower nodes 

 the endodermal pockets are very irregular ; as a rule they 

 have no bottom and often their sides are incomplete. A 

 well-developed pith is present below any trace of internal 

 endodermis not only in sporeling plants but in the basal 

 region of axiliary branches of B. liinaria. Further, 

 the centripetal tracheids forming the mixed pith in B. 

 hinaria {Fig. 5) developed in a young plant above a region 

 where an internal endodermis was present, i.e., in a tissue 

 which on the theory of intrusion would be regarded as 

 of cortical origin. 



These facts are not conclusive, but they show that the 

 presence of an internal endodermis in the Ophioglossaceae 

 cannot be taken by itself as proving intrusion of cortical 

 tissue to form the pith. There is no evidence that this 

 can be established directl)' by the relations of the 

 tissues at the apex during development. The absence 

 of any direct evidence of " intrusion of cortex " holds not 

 only for the Ophioglossaceae but for ferns generally, and, 

 valuable as the concepts of "pocketing" and "cortical 

 intrusion " have been in recent comparative work on 

 the anatomy of ferns, the reality of the tissue changes 



