22 2 
F. W. Oliver. 
the purity of this pollen is a consequence of entomophily rather 
than of anemophily until extensive data are available of the contents 
of wind-supplied pollen chambers and collecting drops in natural 
environments. The mixed pollen in Ginkgo at Montpellier only 
informs us of a vicissitude incidental to existence in a botanic garden, 
whilst the plants of the Palaeozoic grew in natural assemblages. 
It is easy to see why such data are not available. Their getting 
implies premeditated investigation at the right place and time. So 
long as botanists permit themselves to be encumbered with routine 
duties at urban centres during the season of vegetational activity 
so long will such ignorance continue. 
The discovery that pollen may germinate in a foreign pollen 
chamber is not surprising in view of the many analogous records 
among Angiosperms of germination on foreign stigmas. Among 
the fossils the nearest parallel case occurs in a specimen of Physo- 
stoma elegans in Professor Bottomley’s collection at King’s College, 
London. In this section undoubted pollen grains of Physostonia 
have entered not the pollen chamber but the chink or sinus lying 
between it and the base of the whorl of tentacles which forms the 
free part of the integument in this seed. In this position the pollen 
grains have germinated to form bodies which may be sperms. The 
matter was dealt with in my Physostonia paper. 1 
The question of the validity of the presumption that pollen 
present in the pollen chamber of a fossil seed really belongs to the 
plant is of some theoretical importance as it is apt to lead to the 
correlation of detached microsporangia. 2 Seeing that this pollen 
is nearly always pure we may I think with reasonable safety continue 
to draw the accustomed inference until it shall have been established, 
for recent Gymnosperms in natural environments, that foreign 
pollen is liable markedly to preponderate. At the same time such 
conclusions are not infallible, for continuity is the final court of 
appeal, and pollen in a pollen chamber, even if it should have 
developed tubes, does not satisfy the requirements imposed by this 
criterion. 
' Annals of Botany, Vol. XXIII, p. 94, and PI. VI, Fig. 30. 
* Sahni, loc. cit., p. 150. 
