XII EQUISETINEJE 453 



tion of the exact origin of the primary meristem and its relation 

 to the secondary ones found in the branches is much to be 

 desired. 



Jeffrey finds in E. arvense, E. hiemale, and E. limosum, that 

 the neck canal cell usually divides longtitudinally, and compares 

 it with the divisions in the archegonium of Lycopodhim 

 phlegmaria. This division may take place in E. tehnatcia, but 

 is exceptional. It may be mentioned that a similar division has 

 been observed in Mar ait ia Douglasii. 



Each archegonium stands between two lobes, the one from 

 whose base it has itself developed, and the next younger one. 

 As these lobes in vigorous prothallia grow to a large size, and 

 branch, this gives the prothallium an extremely irregular out- 

 line, recalling very much that of Anthoceros pnnctafus or A. 

 fiisiformis. These branching lobes are not to be confounded 

 with the branches of the prothallium body due to the dichotomy 

 of the archegonial meristem. These latter are always short, 

 and project but little compared to the secondary branching lobes 

 produced from them. The entrance of the spermatozoids and 

 the changes subsequent to fertilisation seem to be exactly the 

 same as in Ferns. 



The prothallia are normally dioecious, but this is not ex- 

 clusively the case. To a certain extent the external conditions 

 influence the production of males or females, as in the Ferns,- 

 and unfavourable conditions of nutrition tend to increase the 

 proportion of the former. 



According to Hofmeister (i) the number of archegonia 

 upon vigorous prothallia varies from twenty to thirty. His 

 statement that this exceeds the number of antheridia in the 

 larger male prothallia is not confirmed by Buchtien, who found 

 as many as 120 of the latter in some cases. 



Usually more than one archegonium is fertilised, Hof- 

 meister having found as many a3 seven embryos upon a single 

 prothallium. He does not state how many of these develop. 

 The embryo corresponds closely to that of the Ferns, and has 

 been carefully described by Sadebeck (6). 



The Embryo 



The fertilised tgg grows until it completely fills the ventral 

 cavity, and its granular contents become more separated, and 



