XXVIIl] SEEDS 25 



aggregated into strobili which often bear a close resemblance to 

 seed-cones (fig. 393, A). On a single sporophyll of Cycas circinalis 

 there may be as many as 700 sporangia while in Zamia floridana 

 there are only two microsporangia. The spore-output is large 

 and in extreme cases, e.g. in Dioon spinulosum, the average number 

 of spores in a sporangium is said to be 30,000*. 



Seeds. In the great majority of recent species the seeds may 

 be described as large and afford a striking contrast to the small 

 seeds of the Mesozoic Bennetti tales. A feature of interest from 

 the point of view of comparison with Palaeozoic seeds is the 

 absence of a resting stage, germination in some cases following 

 seed-fall without an interval. As Warming pointed out, the 

 embryo is often undeveloped when the seeds are shed. An 

 interesting fact is recorded by Capt. Dorrien-Smith 2 with regard 

 to seed-dispersal: he describes the heavy pebble-like seeds of a 

 Macrozamia as being hurled from the ripe cones a distance of 12 ft. 

 The seeds of Cycas are platyspermic ; the woody shell exposed 

 on removal of the outer flesh is slightly flattened and has two 

 prominent angles, but three-angled seeds may occur as in Ginkgo 

 biloba (fig. 631, C). In other genera the seeds are radiospermic. 

 The seed of Encephalartos Altensteinii 3 (fig. 396, D) has a square- 

 cut distal end with a small papilla at the summit of the unusually 

 long micropylar canal (17 mm.). The stone of this seed (fig. 396, C) 

 shows parallel curved ridges which mark the position of vascular 

 strands in the inner region of the outer flesh. The large ovules 

 of Cycas circinalis* have an integument 1 cm. thick consisting of 

 an outer and inner flesh and an intervening stony layer which 

 reaches its greatest development at the base and apex. Three 

 vascular strands enter the base of the seed, the concentric strand 

 breaks up in the broad inner flesh into a group of bundles which 

 embrace but do not penetrate the lower end of the nucellus. 

 Each of the two lateral strands branches in the outer flesh near 

 its entrance into the seed; the outer and larger collateral and 

 mesarch bundle passes up close to the surface of the shell to the 

 seed-apex, while the inner branch penetrates the shell and, 

 occasionally branching, passes up the inner region of the inner 



1 Chamberlain (09). 2 Dorrien-Smith (11) p. 287. 



3 Stopes (04) p. 467. 4 Stopes (04) p. 438, fig. 1 ; Warming (77) PL m. 



