March, 1907.] The Embryology of Sagittaria lancifolia. 
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 Nymphceacece f 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 Nymphcea 
advena and the Cuban Nymphcea 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 lancifolia L. for the purpose of comparison 
with S. variabilis Engelm. (now known as 5. latifolia Willd.) as 
studied by Schaffnerj. 
Sagittaria variabilis is distributed throughout the greater 
part of North America except the extreme north and extends 
to Mexico and Florida, while 5. lancifolia 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; S. variabilis extending much 
farther north and S. lancifolia 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 Piperaceae and its bearing 
on the Order. Johns Hopkins Univ., Cir. 178. 29-32. 1905. 
t The Embryology of some Cuban Nymphaeaceae. Botanical 
Gazette, 42: 376-392. 
t Schaffner, J. H.—Contribution to the Life History of Sagittaria 
variabilis. Botanical Gazette 23: 252-273, 1897. 
