BRIEFER ARTICLES 
THE PHYSIOLOGICAL CONDITIONS FOR THE DEVELOP- 
MENT OF MONOECIOUS PROTHALLIA IN 
ONOCLEA STRUTHIOPTERIS! 
The following investigation was undertaken with the view of ascer- 
taining the validity of the statement made by CAmpBELL concerning the 
dioeciousness of Onoclea Struthiopteris. He says: ‘In the genus Onoclea, 
as well as some other Polypodiaceae, the prothallia are regularly dioecious, 
and only a part of them develop the archegonial meristem. The others 
remain one-layered, and are often of very irregular form, and may be 
reduced to a short row of a few cells. All of the ‘ameristic prothallia,’ as 
PRANTL calls them, are males. In the majority of the Polypodiaceae these 
occur more or less plentifully, and are often the result of insufficient nutri- 
tion; but in Onoclea it is something more than this, as not only the small 
prothallia are males, but the large ones are exclusively females, and not 
hermaphrodite, as in most ferns.”? 
The development of fern prothallia, and their reproductive organs, has 
been studied until recently more from the morphological than the physio- 
logical point of view. Much of the work of physiological importance 
demonstrates the effect of various light intensities. PrantL (in 1881) 
was one of the first to investigate carefully the effect of nutrition. His 
observations upon cultures of Polypodium vulgare, Aspidiwm filix-mas, 
Ceratopterts thalictroides, and Osmunda regalis led him to draw the following 
conclusions: that the food supply determines the development of the 
prothallia and the separation of the sexual organs; that good cultural 
conditions favor the production of meristem and the development of 
archegonia; that poor cultural conditions retard the production of meristem 
and favor the development of antheridia; that as nitrogen is one of the 
" requisites of a good cultural condition, an insufficient nitrogen supply May 
be the cause of thickly grouped prothallia bearing only antheridia. 
The spores of Onoclea Struthiopteris used in the experimental work were 
collected from yards about Ann Arbor in September and sown soon after 
t Contribution No. 114 from the Botanical Department of the University of 
Michigan, 
2 Mosses and ferns. Edition 2. p. 314. 
216 
