104 Scott and Maslen . — The Structure of Trigonocarpus. 
An individual sarcotestal bundle is shown, magnified about 200 times, 
in PL XIV, Fig. 28. The position of this bundle is shown at s. b. in PL XI, 
Fig. 5. These bundles are quite small ; the total radial diameter of the 
one figured cannot have been greater than -15 mm., and the diameter of 
the largest tracheide about *025 mm. The bundle is only imperfectly 
preserved, and no trace of phloem elements are visible. The tracheides t 
are nearly in contact with the ordinary parenchyma of the sarcotesta 
sa on the inner side of the bundle, while on the outer side there is a space 
which is partly occupied by decomposed tissue d. t ., which probably 
represents the original phloem elements. The bundle was therefore 
probably a collateral one with external phloem. There is some evidence 
that the xylem was mesarch in structure, as the smaller elements, pre- 
sumably protoxylem tracheides, occupy a more or less central position. 
This conclusion is also favoured by the examination of longitudinal sections, 
as will be explained later (p. 115). This bundle is separated from the 
sclerotesta of the secondary ridge, to which it runs parallel, by sarcotestal 
tissue about -3 mm. in thickness. The longitudinal sections are not 
sufficiently good to enable us to trace the sarcotestal bundles upwards 
to their termination. The transverse section shown in PL XI, Fig. 5, 
cannot be far removed from the middle of the body of the seed, and PL 
XI, Figs. 6-8, and PL XII, Figs. 9, 10, are cut at successively higher levels. 
In all these sections the inner sarcotesta is fairly well preserved, and it seems 
likely that if vascular bundles were present they would have been preserved 
also. No trace of such bundles is visible, so that it seems probable 
that they did not extend farther up than the body of the seed. 
As Trigonocarpus P arkinsoni is the first of the Cycad-like seeds of the 
Carboniferous Period, the Stephanospermeae of Professor Oliver, in which 
it has been possible to give a fairly complete account of the sarcotesta, 
it will be useful to compare this layer with what is known of the correspond- 
ing tissue of other related fossil seeds, and with the ‘ outer flesh ’ of recent 
Cycadean seeds. 
The possession of an outer soft layer to the seed is believed to be 
a common character of all the seeds which constitute Professor Oliver’s 
Stephanospermum-Group of Radiosperms, although in the type genus, 
Stephanospennmn , evidence for its existence, other than from analogy, 
is absent L In most of the genera included in this group, Aetheotesta , 
Trigonocarpus , Tripterospermum , P olylophospermum, Codonospernium , &c., 
an outer fleshy, or sometimes fibrous, sarcotesta has been proved to exist, 
although it is usually very badly preserved. 
Trigonocarpus pusillus , Brongn., a small representative of the genus 
from the French deposits, recently re-described by Professor Oliver, 
possesses a sarcotesta of two or three layers of thin-walled, iso-diametric, 
1 Oliver (’04) ( 1 ). 
