MEDULLOSEAE 457 



originally described by Brongniart, from the Black 

 Pebbles of St. Croix, near St. litienne, of Upper Coal- 

 measure age. It is a comparatively small seed (measur- 

 ing about 10 X 4.5 mm.), and, though the sarcotesta is 

 not preserved, is evidently of the same general type 

 as Trigonocarpus, with which it agrees in the radial 

 symmetry, the prolonged micropyle, the beaked pollen- 

 chamber, and the apparently free nucellus, of which the 

 characteristic tracheal investment forms part. 



The most striking peculiarities of the seed consist in 

 the presence of a prominent ring or collar of the 

 sclerotesta around the micropylar region, and in the 

 nature of the nucellar tracheal system, which forms a 

 continuous mantle of spiral or scalariform tracheides, 

 extending as far as the pollen-chamber and spreading 

 over its floor. 



In this seed the prothallus is sometimes well 

 preserved ; the archegonia appear to have been only 

 two in number ; in the egg-cell the nucleus has been 

 recognised. 



The apex of the pollen-chamber was prolonged into 

 a long beak or tube, engaging with the micropyle (cf. 

 Fig. 170, Trigonocarpus)} Through this beak the 

 pollen-grains entered the pollen-chamber, in which they 

 are found in almost every seed. They also occur loose 

 in the matrix, where they are of small size, averaging 

 only about 60 fi in length, while the average dimensions 

 of those in the pollen-chamber are 160 x 100 /u, (210 /j, 

 being the extreme length observed), so that, as Renault 

 first showed, the pollen-grains developed actively after 



1 In Fig. 173 the conical mass at the top of the figure represents the 

 funnel-shaped base of the tube, but the tube itself is missed. 



