The Ovules of the older Gymnosperms L 
BY 
F. W. OLIVER. 
With Plate XXIV and a Figure in the Text. 
T HE seeds of most recent Conifers are fully siphono- 
gamous, and their organization exhibits an adaptation 
in complete harmony with this type of fertilization — the 
most perfect that has been evolved by aerial plants. But if 
there is any conclusion in phylogeny on which we may con- 
fidently rely, it is that the method of fertilization by pollen- 
tubes has been evolved from zoidiogamy, the type of fertiliza- 
tion characteristic of an aquatic ancestor. The discovery 
of motile spermatozoids in the Cycads and in Ginkgo indeed 
places a coping-stone on the edifice of Hofmeister’s generali- 
zations. 
The pollen-tube of the Conifer affords so simple and direct 
a means of effecting fertilization that we recognize that an 
ovule of relatively simple construction offers adequate facilities 
for the accomplishment of this process. But the instant 
we turn to Cycas or Ginkgo , where zoidiogamy prevails, the 
ovule is seen to be much more complex. Not only do we 
find a special chamber excavated in the apex of the nucellus 
for the reception of the pollen, but the ovule is also provided 
1 This article is based on a lecture delivered by the writer before the Botanical 
Section of the British Association for the Advancement of Science at its meeting in 
Belfast, September, 1902. 
[Annals of Botany, Vol. XVII. No. LXVII. June, 1903.] 
