126 Sahni. — On Certain Archaic Features in the Seed of Taxtcs 
stone in Cycadinocarpus , while in Rhabdospermum they actually turn 
obliquely backwards and outwards to emerge from the stone through two 
foramina not far from the point where the main supply enters the stone. 
For convenience I propose to describe as excurrent and incurrent canals, 
respectively, those channels in the sclerotesta which afford egress or ingress 
to the vascular bundles. 
Now, if we imagine that the outer openings of the excurrent canals of 
Rhabdospermum gradually move forward towards the micropyle, the con- 
ditions observed in Mitrospermum and Taxospermum will successively be 
arrived at : the canals will first become nearly horizontal as in Mitro- 
spermum and then ascending as in Taxospermum . For our purpose the 
most important result of this tendency is that more and more of the ‘ outer ’ 
system of strands becomes included inside the shell-cavity. Thus in Taxo- 
spermum a considerable length of the ‘ outer * system is really inside the 
stone. 
At this point I shall venture a suggestion which at first perhaps appears 
unwarranted, but which, as I hope to show presently, is not entirely without 
a foundation. Assuming that this acropetal tendency on the part of the 
excurrent canals did not become extinct in Palaeozoic times, is it not possible 
that the modern genus Taxus (in which the entire length of the ‘ outer ’ 
system of strands is inside the seed-cavity) may represent the culmination of 
this tendency ? In other words, may it not be that in this plant the excurrent 
canals have actually reached the micropyle and become confluent with it ? 
If this is so, it follows that that part of the stone which in Taxospermum lies 
distally to the excurrent canals (shown solid black in Fig. 7, No. 7) is entirely 
unrepresented in Taxus ; and, further, that the proximal part of the stone 
of Taxospermum (shown dotted) corresponds to almost the whole of the shell 
of Taxus. The single incurrent canal of Taxospermum having split into 
the two incurrent canals of Taxus , that part of the stone of Taxus 
lying between these canals must be regarded as a newly intercalated 
piece. 
Direct comparisons of this nature between plants so widely separated 
in time do not often lead to safe conclusions. But the suggestion here put 
forward is at any rate the only one that affords at all a satisfactory inter- 
pretation of the peculiar seed-structure of Taxus ; and, as we shall see, it 
also makes it possible to compare the latter intelligibly with Torreya . 
When we realize the magnitude of the time-gap between Taxospermum and 
Taxus in the light of this suggestion, the structural gap between them 
becomes surprisingly small ; and the vague comparison which Ad. Brong- 
niart instituted between the two seeds as long ago as 1874, and which he 
expressed in the generic name Taxospermum , now acquires a phylogenetic 
significance. I wish to avoid conveying the impression that I regard 
Taxospermum as being necessarily a direct ancestor of the modern Yew, 
