108 Scott and Maslen.— The Structure of Trigonocarpus. 
On the inner side of the sclerotesta there are three furrows corre- 
sponding in position with the three principal external ridges. These furrows 
vary in depth in different parts of the seed, as is well seen in transverse 
sections. In sections cut across the lower part of the body of the seed, the 
grooves are very slightly developed, and are sometimes absent altogether, 
while in sections taken at successively higher levels, the furrows become 
more and more pronounced. Comparison of PI. XI, Figs. 5-8, will serve 
to demonstrate this fact, as also that the points of the triangular micropylar 
tube are the upward prolongations of the three shallow grooves seen in 
sections across the body of the seed such as shown in Fig. 5. The three 
grooves on the inner side of the sclerotesta, of course account for the three 
ridges which are shown on the surface of the common internal casts of the 
cavity of the seed. 
With regard to the minute structure of the sclerotesta, we have little 
to add to former descriptions. In good thin sections the sclerotesta is 
readily distinguishable into two regions, an inner zone (PI. XI, Fig. 6 , A), 
which is very dark in colour, and consists mainly of elements which are 
elongated in the vertical direction, and an outer zone (Fig. 6, /. f .) in which, 
especially in sections cut across the body of the seed, many of the cells are 
seen to be elongated in a horizontal radial direction, and so form a kind 
of outer palisade layer to the sclerotesta. This is best shown, in Fig. < 5 , in 
the sclerotesta of the secondary ridges. If the section is a thicker one, the 
distinction of the sclerotesta into two zones is not so clearly seen. In more 
detail the structure of the sclerotesta of the central part of the body of the 
seed is as follows. Starting from within, and considering the region between 
the longitudinal ridges, we have first about four to six rows of small 
elongated elements running in the longitudinal direction, and filled with 
the dark-coloured material which is characteristic of all the elements of the 
sclerotesta. These cells are thick-walled and fairly uniform in size, many 
times longer than broad, and of prosenchymatous form. Hooker and 
Binney describe these cells as forming a lining of long slender tubes to the 
whole body of the fruit (i. e. seed), and assert that among these cells some 
maybe found marked with annular or spiral bands 1 . Williamson states 
that traces of the same structure appear in his sections 2 . We have 
examined a considerable number of longitudinal sections of Trigonocarpus , 
including the original Williamson and Hooker and Binney slides, but we 
have been unable to confirm this observation. 
Outside these longitudinally running cells are seen some rows of 
elongated elements which run in a horizontal direction around the body 
of the seed, and outside these is a zone in which the cells appear to meander 
irregularly, the elements passing across one another in all directions. In 
a tangential section of this part of the testa 3 , the elongated cells are seen 
1 Hooker and Binney (’ 55 ). 2 Williamson (’ 77 ), p. 252. 3 Slide 944 S. 
