102 Scott and Mas ten. — The Structure of Trigonocarpus. 
to the concluding part of this paper. The relation of the sarcotesta and 
sclerotesta in Trigonocarpus is such as to indicate that they are mor- 
phologically one integument, just as is the case in the structurally very 
similar layers of a modern Cycad seed. 
Other Palaeozoic seeds also agree in this respect. P olylophospermum 
stephanense (Brongn.), a radiospermic seed from Grand’ Croix which agrees 
with Trigonocarpus in important characters, has been shown by Professor 
Oliver to exhibit gradual transition from the hard sclerotesta to the softer 
enveloping sarcotesta 1 . 
The sarcotesta is bounded externally by the definite limiting layers to 
which Wild first directed attention (p. 95). The figure given by Wild 2 
shows an apparent epidermis consisting of closely set radially elongated 
dark-coloured cells forming a kind of palisade tissue, usually only one, but 
sometimes two, cells in thickness. These palisade cells are covered by 
what is described as a thin cuticle. From the resemblance of this tissue in 
Trigonocarpus to the limiting layer of the petioles of Mcdullosa anglica, in 
which the epidermis has a well-marked palisade form 3 , as well as from the 
constant association of these two forms, Wild was led to believe that 
Trigonocarpus is probably the seed of Mcdullosa. Re-examination of some 
of Wild’s slides shows that some of them exhibit traces of a layer of small 
cells outside the palisade cells, and forming a true epidermis to them. The 
epidermal cells are better seen in some other slides, especially in some of 
those obtained from the Manchester Museum. The limiting layers of the 
sarcotesta is shown in PI. XIV, Fig. 23, drawn from one of the Manchester 
slides, and magnified about 40 times. The epidermis is shown at e, and 
the hypodermis of palisade-like cells at h . The epidermal cells are quite 
small and apparently empty ; their outer walls are thickened to form 
a continuous cuticle which is frequently preserved as a detached line, when 
the radial walls of the epidermal cells are wholly destroyed. The detached 
cuticle of the epidermis is visible in parts of PI. XI, Fig. 1, as well as in 
some of the other photographs in Plates XI and XII. Occasionally the 
epidermal cells are visible in surface view as a simple layer of small 
isodiametric cells. The hypodermis consists of much larger cells usually 
more or less radially elongated and sometimes very irregular in shape 
(PI. XIV, Fig. 23) ; sometimes only one elongated cell appears, elsewhere 
the place of a single elongated cell is taken by a row of two or three short 
cells. All the cells of the hypodermis agree in being filled with dark- 
coloured contents which give to the layer as a whole a very characteristic 
appearance much resembling that of the outer tissues of a Medullosa petiole. 
Re-examination of the Medullosa anglica slides has failed to detect any 
trace of an epidermis outside the rarely preserved palisade tissue which 
apparently includes the real epidermis of this form. At the same time, in 
x Oliver (’04) (1), p. 101. 2 Wild (’00), Fig. 14. 3 Scott (”99), PI. if, Fig. 13. 
