202 SYMMETRY OF THE SPOROPHYTE 
These types of symmetry are not restricted to any of the great groups 
of plants: examples of any one of them may be found in any of the 
great divisions of plant-life. But nevertheless, in certain circles of affinity, 
one or other type of symmetry may be prevalent: thus in the Red and 
Brown Algae the bilateral symmetry is common: among the sporogonia 
of Bryophytes the radial construction prevails: the gametophyte of Liver- 
worts is with very few exceptions dorsiventral. 
The further fact that a single shoot may be at first of one type, and 
subsequently change to another type of symmetry, demonstrates that they 
pass one into another. It can be shown both by comparison and by 
experiment that this occurs within certain limits. The most frequent 
transmutation is that from the radial to the dorsiventral, a change which 
is of special importance in its bearings on the morphology of the 
sporophyte. 
In discussing the subject of symmetry, it has hitherto been usual to 
draw illustrations indifferently, either from the gametophyte or from the 
sporophyte generation. Doubtless, in considering the phenomena of form 
in their general aspects this is right: the wider the net is cast over the 
area of fact, the greater the probability of arriving at a sound conclusion 
as to the qualities and the causes of the several types of symmetry in the 
Plant-body. But it is a different question to enquire into the effect 
which modification of symmetry may have exercised in the evolution of. 
the neutral generation. Analogy, with corresponding phenomena in the 
gametophyte, may assist indirectly: but in the elucidation of the actual 
historical record these can only have a theoretical interest. According 
to an antithetic theory the starting-point of the two generations has been 
quite separate and distinct, and this must have its effect on the study 
of their symmetry. 
In the case of the gam€tophyte various types of symmetry are found 
in the plants of the present day: and since there is no reason to believe 
that there was any common origin of all gametophytes from any one body 
of definite form, there is wide room for speculation as to the source of 
their varying form, and little hope of finality of conclusion. But in the 
case of the sporophyte it is different: the ovum, produced within the venter 
of the archegonium, is normally the starting-point for the sporophyte 
generation in the Archegoniatae: in these plants it is approximately 
spherical in form, and the conclusion follows, on comparative grounds, 
that the initial form of the sporophyte was approximately the sphere—a 
body without polarity and of radial construction. The question to be 
discussed in this chapter is, then, what modifications of forms this simple 
body undergoes in the course of its development into the complex sporo- 
phyte, as seen in Archegoniate Plants; and under what circumstances 
those modifications may have been introduced. 
The development might, in the first instance, consist of simple 
enlargement, together with cell-division, with or without a differentiation 
