62 S a list my. — On the Structure and Relationships of 
shoulders, and the upper again coinciding with the positions of major ribs. 
There seems little doubt, then, that the pollen chamber was three-angled in 
correspondence with the projections of the nucellus lower down. 
VII. Comparison witpi other Types, 
t. T rigonocarpus Parkinson i, Brongniart. 
It is hardly necessary to recapitulate in detail the many points of 
general resemblance which Trigo 7 iocarpus Parkinsoni and T rigonocarpus 
Shorensis have in common. The main structural plan in both seeds is 
essentially the same, but this only serves to throw into greater prominence 
the many differences of their more minute structure. 
We note the entire absence in Trigonocarpiis Shorensis of tertiary ribs 
subtending the vascular bundles, and though the behaviour of the primary 
sutured ribs is alike in each, the beak into which they pass is short in 
T. Shorensis and long in T. P arkinsoni. 
The secondary ribs of the latter seed are subject to considerable 
variation, sometimes being almost absent ; but usually they persist to near 
the apex, where they die out before the micropylar beak is reached, an 
earlier disappearance of the secondary ridges which is still more pronounced 
in T. Shorensis. Scott and Maslen give the thickness of the stony layer in 
T. Parkinsoni as from i to 1*5 mm. (loc. cit., p. 106), which is two to three 
times the corresponding dimension for our seed. Probably this added 
thickness and the increased number of ribs are to be correlated with the 
small extent of the sarcotesta, as compared with that of T. Shorensis , 
necessitating greater mechanical strength in the layer beneath ; or perhaps, 
put more correctly, the broad sarcotesta in the latter species, with its peri- 
pheral sclerotic system, had not involved the necessity for development of 
such mechanical strength in the sclerotesta. 
The most interesting comparison between these two seeds is afforded by 
the sarcotestal structure. This tissue was in T. Parkinsoni bordered at the 
exterior by a narrow epidermis, followed by a thickened palisade-like hypo- 
dermis (Scott and Maslen, loc. cit., p. 102). As we have seen, the limiting 
layers in the present seed were much more complex, and formed a, probably 
anastomosing, complex of radial plates, accompanied by numerous secretory 
elements present also further in, which, though represented, were extremely 
few in T. Parkinsoni. Now the occurrence of radial sclerotic plates at the 
periphery, and of secretory elements both within these and interiorly, are 
characteristic features of the vegetative organs of Medulloseae, and especially 
of their petiolar structure, 1 so that T. Shorensis in this respect would appear 
to be far more primitive than its congener. The absence of the prolonged 
1 Scott, D. H. : On Medullosa anglica. Phil. Trans., B, vol. cxci, p. 101, and PI. VIII, 
Fig. 18, 1899. 
