844 DR R. KIDSTON AND PROF. W. H. LANG ON OLD RED SANDSTONE PLANTS 
place near the beginning of a current of change from an Alga-like type of plant to 
the type of the simpler Vascular Cryptogams.” 
It appears to us unwise to go further than this at present in view of the 
absence of evidence justifying a connection of these Vascular Cryptogams with 
particular Algal forms. We may anticipate sure, if slow, progress in our knowledge 
on this question to come from the fuller study of other plant-remains of this early 
geological period ; caution rather than boldness is therefore advisable in speculating 
on the subject. 
The facts described in these studies of the Rhynie plants, together with other 
recent work on the Early Devonian flora, do not solve the question of the mode of 
origin of the simplest Vascular Cryptogams. It is, therefore, only necessary to 
touch briefly on their bearing upon various hypotheses which have been advanced 
regarding this. It has been pointed out (Part II, p. 623) that the morphology 
of the Rhyniaceae (while not inconsistent with the hypothesis that regards the 
sporophyte as an interpolated phase in the life-history) supports the views which 
hold the sporophyte of the Pteridophyta to have been derived by the modification 
of a plant-body such as is seen in the asexual stage of a number of the higher 
Algae. The former views have been especially worked out by Celakovsky and 
Bower, while the conception of an origin of the Pteridophyta by transformation 
of advanced Algal forms underlies the views of Potonie, Lignier, Schenck, Church, 
and others. It is not necessary to enter here into the details of the various theories, 
which require to be considered in the light of the state of our knowledge at the 
times when they were respectively advanced. 
When the attempt is made to relate in detail any of the particular hypotheses 
to the features of the simple Pteridophyta recently discovered it becomes evident 
how difficult it is to frame such speculations without assuming too much. The 
further knowledge of the course of the life-history in such Algae as Laminaria, 
Cutleria, Dictyota , and the Red Sea-weeds has revealed the existence of a definite 
alternation of generations, with all proportional sizes of the two generations, within 
the Algae. There is thus no reason, as in the earlier statements of the antithetic 
theory, to start with the post-sexual complications in such Green Algae as GoleocJuete. 
On the other hand the absence of leaves and of any specialised root-like branches 
in the Rhyniaceae gives us within the Vascular Cryptogams a simpler starting-point 
for the organisation of the sporophyte than is postulated by either Lignier or 
Church, whose conceptions on the origin of the plant in the Vascular Cryptogams 
by the transformation of an Algal plant-body are the most explicitly formulated. 
The possibility of the type of plant in the Rhyniaceae having been reached by an 
evolution on land, parallel to that of the marine algae, is not to be dismissed as out 
of the question. In this connection some of the conceptions associated with the 
antithetic theory may possibly be found to hold. 
The facts so far known seem to favour the idea of the origin of the land 
