254 GYMNOSPERMJ:. 



quently 5-6) (Figs. 245, 256) ; the same stem produces succes- 

 sively scale-leaves, foliage-leaves, and carpels. The differentiation 

 is not much more advanced than in certain Ferns (Struthiopteris, 

 Blechnuni), where barren and fertile leaves of different form 

 regularly alternate. The other genera have female flowers; the 

 carpels are shield-like in Zamia and Ceratozamia (Fig. 246), 

 and collected into cone-like flowers, which terminate the growth 

 of the stem (Fig. 259). The number of ovules in these instances 

 is two to each carpel. 



The SEEDS are large (most frequently 2-6 centimetres long) and 

 plum-like ; the external layer of the testa is fleshy, while the in- 

 ternal one is hard and horny. There are two systems of vascular 

 bundles in the testa, one outside, the other inside the stone. The 

 embryo is straight, attached to the end of the suspensor, which is 

 often long, filamentous, and rolled up ; it has one or two cotyledons. 



The embryo in Ceratozamia and others is very slightly developed, at the time 

 when the ripe seed is detached from the carpel ; and it is not until after sowing 

 that its further development and germination proceed. This calls to mind 

 the Cryptogams, especially Selaginella, whose macrospores are thrown off filled, 

 with endosperm ; but the oosphere is not fertilised till after the separation of the 

 macrospore from the parent-plant, while in the Cycadeaa fertilisation is effected 

 before the separation. In Cycas the testa may rupture, and the endosperm 

 grow and become green in the light, even though no embryo has been formed. 

 This also is an indication of its prothalloid nature. 



Gum-passages are present in all organs. Collateral vascular bundles, with 

 spiral and scalariform tracheides, are found ; and normal thickening takes place 

 by means of a cambium. An exceptional mode of growth is found in Cijcus and 

 Encephalartos, the cambium ceases to divide after a time and is replaced by a 

 new cambium which arises in the cortical parenchyma just outside the bast, and 

 which forms a new ring of xylem and phloem. This may be repeated so that a 

 number of concentric rings are produced. In Ceratozamia, structures resem- 

 bling corals extend from the roots in a vertical direction and appear on the 

 surface of the soil; these are peculiar roots, in which a symbiotic Alga 

 (Anal/ana) is found. 



The Cycadete were formerly (from the Coal period to the Later Cretaceous) 

 far more numerous than at the present day. They appear to have been most 

 numerous in the Trias and Jurassic. The remnant (75 species) which have 

 persisted to the present time are found in all tropical countries. Cycas (Trop. 

 and Sub-trop., Eastern Hemisphere) ; Dioon (Mexico) ; Macrozamia (Australia) ; 

 EncepJialartos (Trop." and S. Africa) ; Stangeria (Fig. 258, Sub-imp. South and 

 East Africa) ; Bowenia (Trop. Australia) ; Ceratozamia (Mexico, New Granada, 

 Western Brazil) ; Microcycas (Cuba) ; Zamia (Trop. and Sub-trop. N. America.) 



USES. Sago is made from the starch-containing pith of Cycas revoluta and 

 circinalis. The leaves are often used at funerals and church festivals, under 

 the name of " palm-branches." 



