xxvni] 



EBPKODUCTIVE SHOOTS 



23 



aggregated into cones, but in Dioon the strobili are characterised 

 by their more ovoid form and by the looser arrangement of the 

 sporophylls (fig. 386, B), each of which consists of a horizontal 

 stalk expanded distally into a broadly lanceolate upturned end 

 covered with a thick felt of hairs and bearing at its base usually 

 2, rarely 5 — 6, ovules on cushion-like swellings. In Dioon spinu- 

 losum the cones may be 50 cm. long. Between the cones of 

 Microcycas, over 90 cm. long, and those of some Zamias, a few 

 centimetres long, there are many intermediate forms. The 



Fig. 394. Macrozamia Preissii, megastrobilus and (A) single megasporophyll; 

 a, axis of cone ; j), stalk of megasporophyll; «, unripe seeds. (After Eendle.) 



large strobilus of an Encephalartos reproduced in fig. 393, D, 

 shows the convex ends of the sporophylls with a jagged edge, 

 and in monstrous cones the marginal lobes may be abnormally 

 developed and assume the appearance of pinnae^. Each mega- 

 sporophyll bears two large ovules (fig. 393, B). In certain species 

 of Encephalartos the swollen ends of the sporophylls have a trun- 

 cate centre hke the flattened umbo of some Pines (fig. 392, D). 

 The presence of two divergent spines is a peculiarity of the mega- 



1 Thiseltou-Dyer (01); Bot. Mag. 1915, Tab. 8592, 8593. 

 monstrous cones, see Miquel (69), Wieland (02). 



For instances of 



