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-Vaug'han. But since we shall never know the true relations 

 of a plant to its surrounding's 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. 1 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 deeply 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. 



V. 



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. CONARD. 

 GRINNELI,, IOWA, April, 1907. 



