252 Campbell— Contributions to the 
9. The first wall in the embryo is transverse, but may 
be inclined to the axis of the archegonium. The lower cell 
forms the foot ; the upper, stem, leaf, and root. 
10. There is usually, but not invariably, a regular division 
into octants, as in the ferns, and the first divisions in the 
octants correspond also to the fern-type ; but very early all 
trace of growth from an apical cell is lost in all the members. 
11. The leaf arises from two of the upper octants, the root 
from the others, the stem arising between them at a later 
stage. 
12. The growth of the root corresponds to that of certain 
monocotyledons. 
13. More than one archegonium may be fertilized, but so 
far as observed only one embryo develops completely. 
Conclusions. 
On reviewing the statements here given, it is evident that 
Isoetes must still be regarded as holding a very isolated posi- 
tion among plants ; for while showing evident affinities with 
several forms, they are in widely separated groups. 
Vines 1 has given a number of reasons for placing Isoetes 
with the Filicineae rather than with the lycopods with which 
it is generally associated, and calls attention to several points, 
i. e. the anatomy and histology of the stem, the multi-locular 
sporangia, &c., but admits that there are certain difficulties 
in the way. In certain respects, notably the dichotomy of the 
older roots, there is a strong resemblance to the lycopods. 
The secondary thickening of the stem is peculiar among 
living pteridophytes, with the exception of certain species of 
Botrychium , but it is of quite a different type from that of 
gymnosperms and dicotyledons, and approaches more nearly 
that found in a few monocotyledons. 
One point overlooked by Vines, and one it seems to me of 
great importance, is the structure of the spermatozoids. 
These closely resemble those of the ferns, both in their form 
1 Annals of Botany, II. pp. 1 17-2 23. 
