379 
Reply to Criticisms. 
Thus, if we apply consistently to sporangia the same morpho- 
logical methods as to axes or leaves, we shall be prepared to 
recognize in them the possible presence of vascular tissue, and 
the potentiality of branching ; and in my opinion we should 
not be justified in excluding a part from the category of 
sporangia because it shows evidence of branching, or of 
vascular tissue, or even of both together. 
A further factor necessary for my views is the partitioning 
of the sporangium : on this point it is hardly necessary to 
remind readers that partial sterilization of a potential arche- 
sporium has been recognized in the Bryophyta, in Isoetes, 
and in the ovules of various Phanerogams. In particular, 
Professor Goebel has shown that the trabeculae of Isoetes are 
produced from sterilized archesporial tissue, and he allows 
that they serve a useful purpose : but he remarks 1 that he 
would attach only a biological, that is, an adaptive significance 
to the fact that they are the result of partial sterilization of 
the sporogenous tissue, and that it is a question how far 
sterilization may proceed in sporangia and sporophylls. 
I agree with him that this is a question open for discussion ; 
but it appears to me that if sterilized portions of a potential 
sporogenous tissue are admitted to serve a useful purpose, 
and if such occur in forms which we believe to be relatively 
low in the scale of plants, there is a reasonable probability 
that such sterilization will have played a part in the evolution 
of other forms, and it will be our duty to see whether traces 
of similar sterilization occur among other early types. 
Synangia are a marked feature in certain Vascular Crypto- 
gams : they have commonly been looked upon as the result 
of coalescence of sporangia originally distinct ; but I submit 
that it is a possible view that they may have been derived by 
a partial sterilization and formation of partitions in originally 
simple sporangia 2 . It is on grounds of detail of develop- 
ment and comparison of plants akin to one another that 
this question can best be solved : it would be leading us 
beyond the limits of such an article as this to enter now upon 
1 loc. cit. p. 358. 2 See Annals of Botany, v. p. 131. 
