[Vol. 9 



100 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



to the Garden for the use of the excellent collections of Isoetes, 

 comprising the collections of two students of the group, Dr. 



George Engelmann and A. A. Eaton, for the use of the original 

 notes of these workers, and for grants which made it possible to 

 pursue this work. It is also a pleasure to acknowledge the kind- 

 ness of Dr. Wm. R. Maxon, who placed the material of the 

 United States National Herbarium at the writer's disposal; of 

 Dr. Aven Nelson and Dr. C. 0. Rosendahl, who loaned the 

 material from the herbaria of the University of Wyoming and 

 the University of Minnesota, respectively; of Prof. L. R. Abrams, 

 who supplied some west-coast forms from the Dudley Herbarium 

 of Leland Stanford University; of Dr. S. Schonland of Soul 

 Africa, Dr. I). A. Herbert and Prof. T. G. S. Osborn of An tralia, 

 Mr. L. Rod way of Tasmania, and Dr. \V. S. Dudgeon of India, 

 for material of exotic species. 



The writer* has also enjoyed the privilege of examining the 

 sheets of Isoetes in the Gray Herbarium, in the Herbarium of 

 the New York Botanical Garden, and in the Field Museum of 

 Chicago. To those in charge who have facilitated this work, she 

 desires to express her appreciation of the privileges enjoyed and 

 the courtesies extended. 



In the matter of photographic illustrations, the writer is 

 especially grateful for the suggestions and aid given by Dr. J. 

 W. G. Land of the University of Chicago. 



To all others who have by contributions of material, by sug- 

 gestion, or other evidence of interest, added to the completeness 

 of this paper, the writer expresses sincere gratitude. 



' Relationships in Genus 



The species of Isoetes might be considered from the point of 

 view of the sculpture of the megaspore wall as representing a 

 long series from those with simple distinct prominences to those 

 with extended ridges or crests, finally becoming reticulate. In 

 this long series many forms stand out distinctly. But with 

 abundance of material there is- often much evidence of inter- 

 grading between adjacent forms and even of variation within 

 the same species. As an example of the latter, one might cite the 

 case of /. Bolanderi of the west coast of America, a form or- 

 dinarily 1 adorned with 1ow t tubercles, which on occasion fail to 



