94 
PROFESSOR A. ANSTRUTHER LAWSON ON 
through the countless wire-like roots of the fern was rewarded by finding two or 
three prothalli. But this source of material became so laborious, and occupied so 
much time with such uncertain results, that I abandoned it upon discovering the soil 
material. Having found certain localities where very young sporophytes were grow- 
ing in abundance in soil, it became an easy matter to find the prothalli in considerable 
numbers. But the experience of searching in the tree-fern material was by no means 
lost, for during those months of almost fruitless searching I finally learned what to 
look for, and also how to use the searching lenses to the best advantage. My final 
and successful method for locating the prothalli w,as as follows : — I would, in the first 
place, go to a locality where I knew the young sporophytes grew in quantity. 
Certain patches of soil where young plants were just emerging from the soil were 
then selected. At first it was very difficult to distinguish these young plants from 
suckers growing up from old rhizomes, but after some considerable experience I soon 
learned to identify the sporelings at a glance. I would then proceed to lift a patch 
of soil containing the sporelings to a depth of three or four inches. Several such patches 
of soil were taken and carefully placed in pasteboard boxes. These were brought 
home to the laboratory, and practically every particle of soil was closely examined 
with a lens or a binocular microscope. My theory was that where the very young 
sporelings were growing there should also be other prothalli which had not yet 
produced embryos ; for it seemed improbable that the spores, which are produced in 
great numbers, would germinate as isolated individuals. It seemed more probable 
that they would fall to the ground in scattered masses, and the washings of the rains 
would carry them into the interstices of the soil, where they wmuld germinate below 
the surface. This proved to be true, for in almost every patch of soil taken as 
described above, more than one prothallus was found. Three or four were frequently 
found growing close together, and in one case twelve prothalli were found in one 
small pocket of soil. In several instances the prothallus was found still attached to 
the young sporophyte. 
From the numerous examples observed it seems clear that the prothallus of' 
Tmesi'pteris is subterranean. I found none exposed to the light. Some were about 
half an inch deep, but the majority were at least an inch below the surface of the 
ground. They were more freq uently found in wet, sandy soil ; and in many instances 
it was difficult to detect their presence, so closely were they covered with particles 
of sand and the like. The presence of the long rhizoids, and the extension of these 
beyond the immediately surrounding soil, gave the clue to the existence of the 
prothallus. Such small masses of soil were carefully removed and placed in fresh 
water, where they were gently stroked with the fine camel-hair brush until most of 
the soil particles were removed. The destruction and removal of many rhizoids 
during this process was unavoidable. In some cases, however, the particles of soil 
came away more easily, and the natural appearance of the prothallus could be studied. 
In examining the soil with a lens or binocular microscope one frequently meets 
