THALLUS OF SPHAEROCARPOS DONNELLII AUST. 
183 
ventral-posterior. He gives no details as to his method of studying this 
transformation. Campbell also states that the first rhizoid grows from the 
basal cell of the germ tube near the spore wall. It is not usually formed until 
the young plant is multicellular, and it is not separated from the germ tube 
by a wall. Later rhizoids arise from the older cells of the young thallus. 
Goebel's description (7) in general confirms that of Leitgeb. According 
to him, however, it is impossible to say that the thallus develops from a 
single cell of the terminal quadrant of the germ tube, which cell functions 
as an apical cell from the beginning. On the contrary, all the cells of this 
germinal disc take part in the growth of the thallus, an apical cell is dis- 
cernible only at a later stage, and one cannot determine from which cell 
of the germinal disc it was developed. He tends to bring together the two 
opposing views of Leitgeb and Campbell by calling attention to the fact 
that the fo mation of the germinal disc is not the development of a new 
structure from a sort of protonema, but is rather a simple flattening out of 
the young thallus presumably as a response to external conditions of air 
and light. The chief evidence in favor of this idea is found in a comparison 
with the method of growth in regeneration, which may resemble either 
description of the method of spore germination. He contrasts this type 
of development, which he calls "homoblastic," with that of the "hetero- 
blastic" sort, in which the body of the plant arises secondarily from some 
sort of protonema. 
A difference in species may perhaps account for the difference in de- 
scriptions. Campbell, according to Miss Haynes (8), was working with 
either (or both) S. texanus or S. cristatus. The European authors probably 
studied S. Michelii and S. texanus. It is also, of course, not inconceivable 
that differences in climate and in general habit might influence the course of 
development. 
The description which follows is based on a study of sporelings of S. 
Donnellii grown from spores sown broadcast in a mixture of clay loam and 
sand and kept in a Wardian case in the greenhouse. When the young plants 
became visible under a hand lens as minute, bright green growths on the 
surface of the soil, they were picked up with a needle under a binocular 
microscope, the soil was washed off in water, and the plants were mounted 
in glycerin. A solution of chrom-acetic acid (chromic acid, 0.3 g.; glacial 
acetic acid, 0.7 cc; distilled water, 99 cc.) proved most satisfactory for 
fixing. Various attempts were made to stain the sporelings, but without 
much success. They took the stain with difficulty, and it did not prove 
permanent. However, since in most cases the cells were slightly plas- 
molyzed, the cell walls stood out fairly sharply although they did not always 
maintain exactly the original form of the cells. 
Different attempts were made to germinate spores in culture solution, 
using that recommended by Marchal and Marchal (10), but it was im- 
possible to keep the cultures free from fungi brought in on the spores or on 
