6 CYCADALES [CH. 



lateral strobili has recently been described by Chamberlain 1 who 

 figures a stem of Macrozamia Moorei with fertile shoots wedged 

 among the persistent petiole-bases, a condition very similar to 

 that in the Mesozoic Bennettitales. Pearson has also described 

 clear cases of laterally- borne cones in Encephalartos. Cycas 

 exhibits two kinds of branching, the female plants being mono- 

 podial while in the male the branching is sympodial. The micro- 

 spores are produced in sporangia grouped in more or less well 

 defined sori (figs. 389, A; 392, E G). There is no definite 

 annulus, but in the occurrence of groups of thick- walled cells 

 some microsporangia recall those of certain ferns 2 . The ovules 

 vary considerably in size, sometimes exceeding 5 cm. in diameter : 

 there are usually two on each megasporophyll (figs. 393, C ; 

 394 ; 395, 1 d) but in most species of Cycas (fig. 392, B) and 

 occasionally in other genera the number is larger 3 . A thick 

 integument encloses the nucellus with which it is fused except 

 in the apical region (fig. 396, A, B). Below the comparatively 

 long micropylar tube is a well-developed pollen-chamber (fig. 396, 

 B', p), a striking feature of Cycadean ovules, immediately above 

 the megaspore; the latter is filled with prothallus-tissue and 

 bears a small apical group of archegonia on the floor of a depression 

 (fig. 396, A B'). In Microcycas^ as many as 200 archegonia 

 are recorded a very exceptional case and these are not confined 

 to the apical region, though only the apical archegonia are 

 functional. Each archegonium is characterised by a very large 

 oval egg-cell and a much reduced neck 5 . The microspores usually 

 produce a single prothallus-cell, a stalk-cell, and body-cell, and 

 from the body-cell are developed two spirally ciliated spermato- 

 zoids (fig. 396, M). In this respect also the monotypic genus 

 Microcycas is peculiar: it may have as many as 8 body-cells 

 and 16 male gametes in a single pollen-tube (fig. 396, G), while 

 in Ceratozamia 6 4 gametes have been seen in one tube. The 

 pollen-tube grows like a fungal mycelium into the nucellar tissue 

 and the male gametes are formed in the distended proximal end 



1 Chamberlain (13). 2 Lang (97); (00). 



3 Chamberlain (09) p. 410. 4 Caldwell (07). 



6 For figures and references, see Coulter and Chamberlain (10). 

 6 Chamberlain (12) p. 11. 



