March, 1907.] The Embryology of Sagittaria laneifolia. 97 



THE EMBRYOLOGY OF SAGITTARIA LANCIFOLIA L. 



Mel. T. Cook. 



We have been accustomed to base our ideas of the close or 

 distant relationship of species, genera and families on external 

 characters but some of the recent literature on embryological 

 subjects has indicated that the life histories and development of 

 species which are apparently closely related may be quite 

 different. Johnson* calls attention to the wide variations that 

 occur in the development of the tapetum, megaspore, embryo- 

 sac and endosperm in the genera of a single family. In my 

 recent paper on the Cuban NymphcEacecB^ I called attention not 

 only to the difference in character of the endosperm but also to 

 differences in the development of the embryos. This difference 

 was especially interesting in the case of our northern NymphcBa 

 advena and the Cuban Nympho'a which is either a different species 

 or a variety, although the external differences are by no means 

 conspicuous. In the light of these recent investigations it 

 becomes interesting to know to what extent we may expect 

 these differences in the internal life history of the more or less- 

 closely related species and also to know whether these differences 

 co-ordinate with the external differences. This presents the 

 questions: Are embryonic' characters valuable in the separation 

 of species? Are they of phylogenetic importance? 



Recently the author accepted an opportunity to make a 

 study of Sagittaria laneifolia L. for the purpose of comparison 

 with 5. variabilis Engelm. (now known as 5. latijolia Willd.) as 

 studied by Schaffner|. 



Sagittaria variabilis is distributed throughout the greater 

 part of North America except the extreme north and extends 

 to Mexico and Florida, while 5. laneifolia is distributed from 

 Delaware southward and throughout the West Indies. The two 

 species overlap in geographical distribution in the southern 

 part of the north temperate zone; 5. variabilis extending much 

 farther north and 5. laneifolia much farther south. Externally 

 these two species present very striking differences especially in 

 character of the leaves and fruit as shown by the following 

 comparison : 



*Johnson, D. S. — Seed Development in the Piperacete and its bearing 

 on the Order. Johns Hopkins Univ., Cir. 178. 29-32. 1905. 



t The Embryology of some Cuban NymphasaccEe. Botanical 

 Gazette, 42: 376-392. 



X Schaffner, J. H. — Contribution to the Life History of Sagittaria 

 variabilis. Botanical Gazette 23: 252-273, 1897. 



