Contributions to the Life-History of Isoetes. 
BY 
DOUGLAS HOUGHTON CAMPBELL, 
Professor of Botany in the Indiana State. University .. 
With Plates XV, XVI, XVII. 
S INCE Hofmeister first called attention to the homologies 
existing between the heterosporous pteridophytes and 
the spermaphytes, the genus Isoetes has always been an object 
of special interest to botanists, and the subject of numerous 
investigations, as it is, in some respects, undoubtedly the 
nearest to the spermaphytes among all known living pterido- 
phytes. For this reason a thorough study of the life-history 
of some species, as compared with other pteridophytes, has 
long been a desideratum, both as a means of determining to 
which class of the pteridophytes Isoetes is most nearly allied, 
as well as, if possible, to throw some light upon the origin of 
the spermaphytes. 
The mature sporophyte 1 has been thoroughly studied, and 
the development of the sporangia and spores 2 has been care- 
fully investigated. Since Hofmeister’s 3 work, however, but 
little has been done upon the female prothallium ; but Mil- 
lardet 4 , and later Belajeff 5 , have described in detail the 
germination of the microspores and the development of the 
1 Hofmeister, De Bary, Brachmann, See. 
2 See especially Goebel, Beitrage zur vergleichenden Entwickelungsgeschichte 
der Sporangien, Bot. Zeit. 1880-1881. 
3 Hofmeister, Higher Cryptogamia, pp. 336 ff. 
4 Le prothallium male des crypt, vase. 
5 Belajeff, Bot. Zeit. 1885, pp. 793-809. 
[Annals of Botany, Vol. V. No. XIX. August 1891] 
S 
