Oliver . — The Ovules of the older Gy mno sperms . 455 
period of maturation, and in due course liberated free-swim- 
ming spermatozoids. It is true spermatozoids have never 
been certainly recognized in these seeds, but that is a matter 
of small importance. The apex of the nucellus of Cycas and 
Ginkgo is similarly organized as a pollen-chamber, and in 
these cases it is well known that spermatozoids were liberated. 
But Stephanospermum is an older seed and exhibits more 
primitive characters than do the Cycads. Were fertilization 
effected by pollen-tubes the whole structure of the seed would 
be a contradiction. Whether or no the discharge of spermato- 
zoids was accompanied by pustule-like projections from the 
surface of the grain is an open question. Such projections, 
very small in relation to the diameter of the pollen-grain, 
have been occasionally observed. The stage at which almost 
all these seeds have been preserved is that just preceding 
fertilization ; only occasional specimens being met with in 
a slightly earlier stage of development. In referring to them 
the term seed is usually employed, though in recent Gy mno - 
sperms the corresponding stage would be called an unfertilized 
ovule. This usage in terminology has doubtless arisen from 
the appearance of maturity which their integumentary tissues 
present, a maturity which seems to preclude all possibility of 
subsequent expansion. In course of evolution, probably, the 
time of hardening of the integument was postponed till 
embryonic stages had set in, so that well-marked ovular and 
seed phases became recognizable ; but in the palaeozoic seeds 
known to us such a distinction can hardly be drawn. 
Whatever their differences in detail, the Radiosperms agree 
in that the nucellus is invested in a tracheal mantle or a 
number of tracheal strands, which, arising from the chalazal 
bundle, meet below the pollen-chamber, the floor of which 
they seem to have paved. Nor does their function seem 
difficult of interpretation. It was that of a mechanism for 
bringing water to the pollen-chamber. This would be impor- 
tant during the period of pollen-maturation and vital to the 
transport of motile spermatozoids at fertilization. 
The pollen-chamber shows every indication of having been 
