MAY 1 1899 



5. The Development, Structure, and Affinities of the Genus Ecjuisetum. 



By Edward C. Jeffrey. 



(Read March 15, 1899.) 



Introductory. 



De Bary in his masterly Coiiiparative Anatomy of the Vegetative Organs of Vascular 

 Plants expressly renounces the consideration, of what he terms the i^oir vettir, the course 

 of development, and practically confines his attention to the structure of mature orijans. 

 It rnay be assumed, that this was done more to limit a task which he describes as a labor 

 (jf tlie Danaids, than from iiny real distrust of the developmental methods, which yielded 

 in his hands such splendid and lasting results in the study of Fungi. Since the appear- 

 ance of De Bary's text-book there have been many researches on tlie development of the 

 sporangia, spores, prothallia, archegonia, antheridia, embryos, and meristemata of vascular 

 plants, and on the mature structure of their le.ss accessible tropical representatives, and 

 the still rarer fossilized remains of past ages; but in the midst of all this acti\-itv one 

 developmental study has been almost entirely overlooked. 



In his presidential address before the botanical section of the British association for 

 the advancement of science, at the meeting of 189('), Dr. D. H. Scott (p. 2) makes the 

 following remarks : - — " The embryological method has so far received scant justice from 

 botanists. * * * In the cases which have been investigated perhaps excessive attention 

 has been given to the first division of the ovum, the importance of which, as Sachs 

 showed long ago, has been overrated, while the later stages when the diffei-entiation of 

 organs and tissues is actually in progress have been comparatively neglected."' 



Convinced of tlie truth of this statement, the writer has devoted considerable atten- 

 tion to the study of the development of the young sporophyte, in all the various groups 

 of vascular plants and his investigations have led to conclusions, which seem to have a 

 not unimportant Ijearing on certain problems of the morphology and phylogeny of the 

 phanerogams and vascular cryptogams. 



The present memoir is devoted to the development and structure of the genus Equj- 

 setum alone ; but in order that the questions presented by the ontogeny and anatomy of 

 the Equisetaceae may be fully appreciated, it is necessary to indicate in a general way the 

 relevant morphological conceptions which now prevail, and to state as In'iefly as possible. 



