8 4 
F. Cavers. 
THE INTER-RELATIONSHIPS OF THE BRYOPHYTA, 
By F. Cavers, D.Sc. 
XI. RELATIONSHIPS OF BRYOPHYTA 
TO OTHER PHYLA. 
N the foregoing study of the morphology and inter-relationships 
of the Bryophyta, it has been assumed, as a working theory, 
that the Bryophyta, as arranged in the scheme of classification 
that has been outlined, in reality form an ascending series marked 
on the whole by progressive elaboration of the sporophyte; that 
the sporogonium of the Bryophyta has arisen as an interpolated 
generation, with gradually increasing “ sterilisation of potentially 
sporogenous tissue,” from the segmented oospore; that though the 
archaic condition in which the sporogonium was a simple spore- 
fruit, consisting of a mass of sporogenous cells enclosed in the 
venter of the fertilised archegonium, is not actually realised in any 
known Bryophyte, we have in the Riccia capsule a primitive 
sporophyte in which sterilisation has proceeded only as far as the 
formation of a single peripheral or epidermoid cell-layer constituting 
the capsule-wall; that the Riccia type of sporogonium is therefore 
not only the simplest but the most primitive known to us. 
The view that the simple types of sporogonium found in Riccia, 
Corsinia, and the Sphaerocarpales are not primitive, but reduced, 
would involve the assumption that extensive and far-reaching 
reduction has taken place in the evolution of the Bryophyta. 
Goebel has recently, in his memoir on Monoselenium to which 
reference has already been made, put forward the view that the 
Marchantiales constitute a descending series of reduction forms, 
starting from a Marchantia- like type, and that Riccia represents 
the lowest and most reduced member of this series. There can be 
no doubt that certain features in the morphology of Monoselenium, 
Cyathodium, Monoclea, and Dumortiera, all belonging to the 
Marchantiales, are best explained as reduction phenomena 
correlated with adaptation to moist and shaded habitats. As 
might be expected, the different organs exhibit different degrees of 
reduction. In Monoclea the thallus shows complete reduction of 
air-chamber tissue, along with almost entire abortion of the scales 
and tuberculate rhizoids characteristic of Marchantiales, but the 
sporogonium is highly developed, and instead of showing the 
slightest sign of reduction, differs from that of all other Marchan¬ 
tiales in having a long seta which raises the capsule well above the 
