Notes, 
2 55 
phyte and sporophyte and the early stages of vegetative buds 
re-assume the prothalloid form is worthy of note, as bearing on some 
cases of apospory. 
These departures from the normal development of the prothallus 
are not regarded as reversions in the ordinary sense, but as indica- 
tions of the capability of direct response to altered conditions 
possessed by the gametophyte. Their possible importance in relation 
to the theory of homologous alternation appears to the writer to be 
of this nature. If that theory be true, the sporophyte and gameto- 
phyteare modifications of a similar form. The gametophyte, especially 
the simple free living prothallus of the Ferns, has departed less 
widely from that form. Such an organism as a fern-prothallus would 
therefore appear to be suitable for experimental work, in the hope that 
its behaviour under altered conditions would afford hints as to the sort 
of changes which, in the original algal form, led to the evolution of the 
sporophyte. The altered conditions in this series of experiments are 
of a similar kind to those which are assumed by Professor Bower to 
have occurred on the spread of algal forms to the land, and to have 
conduced to antithetic alternation. 
The results may now be used in picturing the manner in which 
alternation of generations might have come about by the modifica- 
tion of originally similar individuals into gametophyte and sporophyte. 
It is assumed for this purpose that the sporophyte of the Vascular 
Cryptogams did not arise by the elaboration of a structure resembling 
a bryophytic sporogonium. It is recognized that the theory of 
antithetic alternation, as elaborated by Professor Bower, affords a 
consistent and satisfactory explanation, if the assumptions necessitated 
by the theory are granted. The present theory, which is put forward 
merely as a provisional hypothesis, is founded on another class 
of facts. 
With the spread of algal organisms to the land, where in the 
absence of any vegetation affording shade some at least would be 
exposed to more intense illumination, the flattened form would 
probably be assumed. Prolonged drought and the influence of direct 
sunlight, inducing directly a change of form into a cylindrical 
body, might be accompanied by the substitution of a reproductive 
organ forming dry reproductive cells (spores) for those adapted to 
an aquatic existence. The acquisition of more highly developed 
absorbent organs (primitive roots) would further the existence and 
