SHOWING STRUCTURE, FROM THE RHYNIE CHERT BED, ABERDEENSHIRE. 623 
stage in the organisation of the sporophyte of Vascular Cryptogams. On grounds of 
their general structure it may be presumed that these simple plants were land plants. 
They are somewhat advanced along the line of progression of the land-growing 
sporophyte, but not so far as to obliterate clues to the origin of this. 
Speculations as to the origin of the sporophyte of the Pteridophyta when broadly 
considered fall into two groups. On the one hand, it has been suggested that the 
vegetative organs of the sporophyte have arisen as the result of a process of pro- 
gressive sterilisation within an interpolated phase of the life-history ; this phase in 
its simplest form was composed wholly of reproductive spores. On the other hand, 
the origin of the sporophyte of the Pteridophyta has been looked for in the modi- 
fication of a plant body such as we see in the asexual stage of a number of Algae ; 
this would have a more or less differentiated vegetative portion bearing asexual 
reproductive organs. 
It appears to us that, while not inconsistent with the first of these two hypo- 
theses, the morphology of the Rhyniaceae is much more in line with the second. 
The organisation of Hornea and Rhynia make the transition assumed by this second 
hypothesis readily conceivable. 
We do not, however, desire to enter at present into a discussion of the general 
problem or to draw conclusions that would be premature. The interest of Rhynia 
and Hornea lies in their providing new and definite historical data on early steps 
in the evolution of land plants. Since we may hopefully expect further dis- 
coveries to make the story more complete, any hypothetical construction of the 
course of evolution would be superfluous. It is sufficient, without entering into 
particular theories, to have indicated the bearing of the new facts on some of 
the chief hypotheses as to the early steps in the origin of land plants that have 
been entertained by morphologists. That these archaic and simple Pteridophyta 
should compel us to institute comparisons, not only with some existing Vascular 
Cryptogams but with bryophytic sporogonia and the organisation of the plant 
in some Algse, appears to us pregnant with morphological interest whatever the 
actual lines of descent may have been. 
EXPLANATION OF PLATES. 
(All the figures are from untouched photographs.) 
Plate I. 
Rhynia Gwynne- Vaughani, Kidston and Lang. 
Fig. 1. A small rhizome ( r .) in transverse section attached by rhizoids (rh.) and giving off laterally an 
ascending stem ( br .). x 14. (Slide No. 2423.) 
Fig. 2. Longitudinal (a) and transverse ( b ) sections of apical regions of stems. x 14. (Slide No. 2425.) 
Fig. 3. The longitudinal section of the apex of a stem shown in fig. 2 (a), more highly magnified, x 105. 
(Slide No. 2425.) 
