MARCHANTIALES 259 
primitive type, though the suggestion has also been made that it may 
really be reduced; but in view of the fact that the gametophyte in the 
Ricciaceae is a well-developed structure, amply capable of nourishing not ’ 
only one but many such sporogonia, there appears no immediate reason to 
hold that this sporophyte is other than primitive in its simplicity. The 
points of special interest in it for the purposes of comparison with the 
more complex Archegoniatae are these: that it shows no distinction of 
apex and base: that the whole central mass of cells is fertile, each cell 
producing spores, while none are diverted to purposes of nutrition or of 
a7 Go: 
we er 
Ricctocarpusnatans. The upper figure 
Fic. 119. shows the spherical spore-mother-cells 
The nee : surrounded by nutritive material. The 
Ricciocarpus natans. Young sporogoniain longitudinal section, lower shows the tetrads formed from 
surrounded by the archegonial wall. The younger (*666) shows them: the sporogonial wall (shaded) is 
the amphithecium (shaded) surrounding the sporogenous cells: in _ still seen surrounding them, and covered 
the older (560) these are separated, as the free, and rounded _ externally by the archegonial wall of two 
spore-mother-cells. (After Garber.) cell-layers. 666. (After Garber.) 
dispersal: and that the superficial cells forming the wall are segmented off 
by periclinal walls of relatively late origin, indicating some _ relatively 
recent differentiation of them from the cells which lie within. 
A reasonable theory of the phyletic origin of a simple sporogonium, 
such as that of Azccia founded on these facts, would then be, that it 
sprang from the simple zygote, as in point of fact all normal sporophytes 
do. The simplest possible case of a sporophyte would be that the 
chromosome-reduction which follows on fertilisation should take place on 
the first segmentation of the zygote, and in certain Algae this appears 
actually to occur (Chapter V.). But in the sporogonium of Avzccra the 
reduction which accompanies tetrad-division is held over till a limited 
number of segmentations of the zygote have been completed: this suggests 
