Notes. 
167 
further removed from this position as the process continued to increase 
in length. It is uncertain whether this growth is by direct continua- 
tion of the original growing-point of the process, or whether the 
development of a group of sporangia at the apex necessitates the 
formation of a new growing-point; possibly both forms occur. If 
the latter be the case, a process on which several groups of sporangia 
are present must be looked upon as a sympodium. Some probability 
is lent to this view by the fact that the first appearance of the 
process in Lastraea is usually as a sympodial continuation of the axis 
of a prothallus whose true apex has developed one or more sporangia. 
Since the group of sporangia and the tissue of peculiar character 
on which they are seated are developed in the place of an apoga- 
mously produced vegetative bud, they may be looked upon as con- 
stituting a very reduced sporophyte. The drain upon the resources 
of the prothallus entailed by the production of this reduced bud, 
which is incapable of further growth, is much less than when a 
vegetative bud is formed. This explains why a number of such 
sporangial groups can be produced and supported by a single pro- 
thallus. The occurrence of a number of vegetative buds on a single 
prothallus is the exception, but may happen, as the case of Aspidium 
frondosum , before mentioned, shows. 
It is probable that it is in the constitution of the nuclei that a means 
of distinction between cells of the oophyte and the sporophyte must 
be looked for in these cases in which the two generations are in 
intimate connexion with each other 1 . 
The complete life-history of the Fern is in these cases still further 
shortened than in the ordinary cases of apogamy ; not merely the 
formation of a zygote by the fusion of antherozoid and ovum, but 
the formation of an embryo, in which any differentiation of the 
vegetative organs can be detected, is omitted, and the sporophyte 
is reduced to a mass of tissue which may be compared to a placenta 
bearing sporangia. The occurrence of single sporangia upon the 
edge of the prothallus may, in the light of the series of stages 
described, be considered as a still further case of reduction of an 
apogamous sporophyte. While this does not altogether prevent the 
explanation of the presence of sporangia upon the prothallus from 
the point of view of the supporters of the homologous nature of the 
1 Bower, Trans. Bot. Soc. Edinb., Vol. xx. 
