THE ORIGIN OF HETEROSPORY IN MARSILIA 
CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY 133 
CHARLES H. SHATTUCK 
(WITH PLATES II-VI AND ONE FIGURE) 
Much morphological work has been done among the heterosporous 
pteridophytes, but they have not been subjected to experimental 
methods to obtain some suggestion as to the origin of heterospory. 
From certain phenomena that I observed in making a morphological 
investigation of Marsilia quadrifolia, it seemed possible that an experi- 
mental study might furnish some evidence as to the way in which the 
heterosporous habit began in this form. 
Historical 
The natural presumption has been that the Marsiliaceae have 
sprung from a homosporous ancestry, but there is little definite evi- 
dence to substantiate this view. CAMPBELL (4) has suggested that 
a near relationship exists between Marsiliaceae and Schizaeaceae. 
Bower (2) calls attention to the striking morphological resemblance 
between the sporocarp of the Marsiliaceae and the spike of Ophio- 
glossaceae. 
JOHNSON (14), GOEBEL (11), and others have pointed out features 
suggesting that Marsiliaceae are not far removed from the homo- 
sporous ferns, but apparently no experimental work has been done 
which might show that the Marsiliaceae were originally homosporous 
and by what process they have attained their present heterosporous 
condition, or in fact how this condition has arisen in any other form. 
In 1887 BucHTIEN (1) called attention to the fact that in Equise- 
tum the sex of the prothallium is controlled very largely by nutrition, 
and drew the conclusion that dioecious prothallia are an indication of 
incipient heterospory. This view will be discussed later. 
The first literature bearing directly upon the origin of heterospory 
appeared in 1894. WILLIAMSON and Scorr (24, 28), in their work 
on Calamaria, were the first investigators to offer a tenable theory. 
After an extensive study of two species of Calamostachys, in which 
Botanical Gazette, vol. 49] [19 
