290 TRANSACTIONS OF THE CANADIAN INSTITUTE. [VOL. V.^ 



anything of the embryology was known. In the homosporous LycopodinecB 

 the apex of the stem, the cotyledon, and the root, are all according to 

 Treub's description, derived from the hypobasal half of the embryo. In 

 Isoetes, echinospora, the same three organs, according to Campbell's 

 account, originate from the epibasal octants, the foot being formed 

 from all the hypobasal octants. No recent coftiplete investigation 

 of the embryology of the SelaginellecE is available, but the phases 

 of development described by Pfeffer can only be harmonized with the 

 octant theory by something like a tour de force. In the EquisetacecB, 

 according to Sadebeck, the shoot originates from the upper octants, and 

 the root and foot from the lower octants, the primitive leaves being 

 derived secondarily from the shoot meristem. The Ophioglossacece, as 

 represented by B. virginianiirn resemble embryologically Isoetes echino- 

 spora. The segmentation of the Marattiacece alone, agrees fairly well 

 with the stages of development found in the leptosporangiate Filicinece, 

 and it is not very difficult in this group to refer the organs to definite 

 pairs of octants. But of all the eusporangiate forms, the Marattiacece 

 come closest to the leptosporangiates, and this probably is the explana- 

 tion of their embryological agreement. 



If we are to accept the hypothesis that the eusporangiate Pteridophyta 

 are primitive, and if we follow Bower in deriving their sporophytic 

 phase from the progressive sterilization of the potential sporogenous 

 tissue of intercalary sporogonium-like forms, the axis is certainly to be 

 regarded as primitive, and the leaves and roots must be considered as 

 secondary outgrowths from the axis ; either by eruption as Bower sur- 

 mises, or by some other undiscovered process. According to this con- 

 ception, foot and shoot are the primitive organs, and leaf and root are 

 subsequently derived from the latter. This view of the matter har- 

 monizes with what is known of the embryology of the lower eusporan- 

 giates. In the highly specialized leptosporangiates on the other hand, 

 a process of acceleration and rearrangement has been carried out and 

 the organs appear precociously, in definite relation, to the earlier 

 segmentations of the embryo. 



In conclusion, the writer wishes to express his special obligations to 

 Professor G. L. Goodale of Harvard University for very kindly putting 

 at his disposal the books of the Gray Herbarium. 



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