SUBKINGDOM SPERMATOPHYTA 



327 



The habit of the sporophyte in the Cycads is fern-like, and one 

 species, Stangeria paradoxa, was actually first described as a Fern. 

 The large pinnate, or in Bowenia bi-piiiuate, leaves spring from the 

 summit of a trunk, which may be cylindrical and several metres in 

 height, or is short and almost globular. The leaves may form a close 

 crown, like that of a Palm, or they may be few in number. In the 

 former case e.g. Cycas they are formed in series, a whorl of foliage- 

 leaves, which unfold simultaneously, alternating with a whorl of 

 scale-leaves, the arrangement being much like those in certain Ferns 

 with regular periodic growth, such as Struthiopteris Germanica. The 

 young leaves in Cycas (Fig. 289) have the pinnae coiled inward, very 

 much as in the Ferns. The leaflets may have a single median vas- 

 cular bundle, as in Cycas, but usually there are several veins, which 

 either run parallel 



A 



F 



or, in Stangeria, are 

 forking, like those in 

 the leaves of many 

 Ferns. 



The Stem 



The stem may remain 

 unbranched, but in the 

 large species, especially 

 Cycas revohita, the older 

 plants are frequently 

 branched, this looking 

 as if it were the result 

 of dichotomy. Small 

 adventitious buds are 

 often formed in large 

 numbers at the base of 

 the stem, usually from 

 the leaf-bases. There is 

 a secondary growth in 

 thickness in the stem, 

 but it is very slow, so 

 that the stem increases 

 but little in diameter 

 after the crown of leaves 

 has attained its full size. 



Histology of Stem. The growth of the stem-apex is due to a group of initial 

 cells. The stem shows a large central pith about which is arranged a circle of 

 collateral bundles, very much as in the stem of Botrychium, and the bundles 

 show a slight development of secondary wood, due to the activity of the cam- 

 bium ; but a large part of the stem is composed of fundamental tissue. The 

 cambium, in Cycas, finally ceases its growth, and a new cambium-ring is devel- 

 oped in the cortex, outside the ring of bundles, and this gives rise to a second 

 ring of wood and bast. This is repeated, resulting in alternating rings of wood 



FIG. 290. A, Cycas circinalis, sporophyll with ovules, o 

 (X i). B-E, C. revoluta. B, section of young ovule 

 (natural size) ; ma, macrospore (embryo-sac). C, 

 sporophyll with microsporangia (pollen-sacs), mi 

 (Xi). D, sorus of microsporangia, enlarged. E, ripe 

 pollen-spore (x 400) ; an, antheridium. F, G, Zamia 

 integrifolia. F, female cone (X 3)- O, sporophyll 

 with two macrosporangia (X 1). 



