IOI 
Scott and Mas leu . — The Structure of Trigonocarpus. 
walled cells abut quite suddenly on the dark-coloured thicker-walled 
elements of the sclerotesta (PL XI, Fig. 5). The outer portion of the 
sarcotesta appears to have been .lacunar, which fact helps to account for 
the almost complete destruction of this tissue. The lacunar zone is 
occasionally preserved to a slight extent in the bays between the longitudinal 
ridges of the sclerotesta. PI. XIV, Fig. 24, shows the lacunar sarcotesta in 
one of Williamson’s original slides, and a similar tissue can be made out 
in several sections belonging to the same series. 
It has been stated above that the sarcotesta is sharply delimited from 
the sclerotesta ; the sudden transition is well seen in sections passing across 
the central part of the body of the seed, such as that shown in PL XI, 
Fig. 5. A section showing the details of the structure of the inner 
sarcotesta and outer sclerotesta, such as that figured in Williamsons paper 1 , 
shows that the sharp demarcation is not simply the result of thickening of 
the walls of the elements of the sclerotesta, for the radially elongated cells 
of the outer part of the sclerotesta abut suddenly on the rounded cells of 
the sarcotesta, so that there is seen to be a difference in the form of the 
elements as well as in the thickening of the walls. 
In transverse sections passing across the lower part of the seed, such 
as are shown in PL XI, Figs. 1 and 3, the transition from sclerotesta to 
sarcotesta is much more gradual. In Fig. 1 the sclerotic tissue is seen 
surrounding a triangular space b enclosing the incoming vascular bundle : 
this dense tissue passes over quite gradually into the surrounding thin- 
walled sarcotesta. In Fig. 3, which is cut at a somewhat higher level across 
the same seed, the outermost sarcotestal cells are seen to be quite thin- 
walled, but nearer to the central sclerotesta t. the walls become thicker 
and the transition is more or less gradual. 
Sections across the upper part of the seed also show a more or less 
gradual passage between the two layers, as will be seen by examining 
PL XI, Figs. 7 and 8, and PL XII, Fig. 9, which are transverse sections 
cut at successively higher levels across the micropyle. 
The absence in certain regions of sharp demarcation between the two 
layers of the testa is of interest in the comparison of Trigonocarpus with 
the seeds of Cycas and other recent forms of similar organization. Miss 
Stopes has shown that it is usually difficult to draw a boundary line 
between the outer flesh and the stone layers in a modern Cycadean seed, 
and she insists that the stone layers, or at least the outer part of them, 
belong morphologically to the outer flesh and so form one layer, not two 2 , 
We shall leave the further discussion of the bearing of this question of the 
single or double nature of the Cycadean integument, and the attempt to 
explain the complicated integument of a Cycad ovule as the morphological 
equivalent of a Lagenostoma with the cupule and integument fused together, 
1 Williamson (77), PI. 14, Fig. 112. 2 Stopes (’05), p. 562. 
