F. E. Fritsch 
170 
of the organisation of a land-plant, the anatomy of its tissues, the 
morphological differentiation of members, as also the otherwise 
wholly inexplicable sequence of sexual and asexual phases in the 
life-cycle, are the expression of response to the conditions of marine 
environment/’ It is difficult to conceive of any factor or group of 
factors in marine environment that could be interpreted as especially 
stimulating evolution in these directions. Is it not more likely that 
the equipment evolved alike in the sea and in the land-flora is an 
expression of the general trend of evolution in vegetable organisms? 
Among Seaweeds (Siphonales, Ectocarpales, Florideae) a massive 
soma has been evolved from the primitive filamentous condition by 
several different methods, and are we to suppose that marine environ¬ 
ment alone stimulates such evolution and that an analogous origin 
from simple filamentous forms would be impossible on land? As 
regards morphological differentiation of members, a flattening of 
certain portions of the shoot-system for purposes of photo-synthesis 
is surely a response which can be postulated as readily under 
terrestrial as marine conditions, and is indeed observed in many 
“xerophytes” as cladodes and phyllodes, undoubtedly evolved on 
the land; such flattening is moreover evident in the terrestrial 
Prasiolae. Development of branches (axillary only in Phanerogams 
and a few others), in close connection with such foliar expanses, is 
probably a necessary physiological consequence of the localised 
assimilatory activity. A somatic main axis once established, its 
downward growth into the soil as a root is not difficult to conceive 
without the necessity of supposing a derivation from the “ crampons ” 
of present-day Seaweeds. If Rhynia and Psilophyton are to be 
regarded as primitive Pteridophyta, it is possible that in some of the 
transmigrant races at least the establishment of roots and leaves was 
deferred to a fairly late stage. 
An alternation between sexual and asexual phases must have 
come about as soon as the reduction-division became associated with 
spore-formation, for when the spores were haploid the plant to which 
they gave rise (gametophyte) was cytologically different from the 
other (sporophyte). Need we assume that such relegation of the 
reduction-division to the time of spore-formation could only occur in 
the sea? There does not appear to be any logical reason for such an 
assumption, since we know of nothing in marine environment that 
would specially favour such a direction of evolution. The fact that 
it exists in many Brown and Red Algae may be taken as merely 
showing that it is an inevitable trend of evolution in all advancing 
