PREFACE. 
Aside from certain personal interests and opinions, the impulse to the 
present investigation came from a study of recent papers by Jeffrey, Boodle, 
and Gwynne-Vaughan. But since we shall never know the true relations 
of a plant to its surroundings until we have worked out its complete life- 
history, it seemed to me very desirable to have all of our knowledge of 
this species collected into a unit. Therefore the study was carried beyond 
the problems suggested by the papers referred to. 
The work was begun in odd moments of an instructorship at the Uni- 
versity of Pennsylvania, but nearly all of it was actually done in the 
Botanical Laboratory of the Johns Hopkins University, and this paper is to 
be regarded as Contribution No. 7 from that Laboratory. I was there as 
“James Buchanan Johnston Scholar’? from February, 1905, until June, 
1906. For the opportunity to carry on this investigation in a peculiarly 
stimulating atmosphere, I am decply indebted to those who administer 
the affairs of the university. It is an especial pleasure to express appre- 
ciation of the constant friendly interest taken by Prof. Duncan S. Johnson. 
The fundamental teachings of Prof. W. K. Brooks have also molded many 
of my thoughts and expressions. Thanks are due to Mr. I. F. Lewis fora 
collection of material from Long Island; to the late Mr. E. R. Heacock for 
my first pot of prothallia and “‘sporelings;’’ to Dr. C. E. Waters for infor- 
mation and for the excellent photographs, plates 1 and 2; to Henry Holt & 
Co. for the use of two copyrighted pictures; to Capt. John Donnell Smith 
for library facilities; to Mr. J. D. Thompson, of the Library of Congress, 
and Mr. Joseph H. Painter and Mr. W. R. Maxon, of the United States 
National Museum, for looking up certain papers not otherwise accessible 
to me; and to the officers of the Academy of Natural Sciences of Philadel- 
phia for the use of several rare old books. All of these obligations are now 
gratefully acknowledged. 
Henry S. Conarp. 
GRINNELL, Iowa, Afrz/, 1907. 
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