GROUP IV. PHANEROGAM1A: GYMNOSPERJLE : CONIFERS. 



481 



on the under surface, usually numerous (2 to 1000) microsporangia, either 

 scattered or in sori (Cycas, Stangeria, Zamia). The macrosporophylls bear 

 two orthotropous macrosporangia, one on each flank, developed upon the peltate 

 terminal lamina ; but the exceptional macrosporophylls of Cycas (see Fig. 303) 

 may bear as many as five macrosporangia. 



The macrosporangia are all sessile, and have a single integument, and are of 

 considerable size ; those of Cycas are as large as a plum before fertilisation. 



In the coniferous genera, the macrosporangiate flower becomes the fruit ; 

 that is, a dry cone, the sporophylls of which fall away, and so set free the 

 seeds In Cycas, the sporophvlls bend outwards and drop off, bearing the 

 seeds. The seed is covered by a testa, developed from the integument of the 

 ovule, which is succulent externally and stony internally. It contains a single 

 straight embryo, on a coiled suspensor, lying in the endosperm. The embryo, 

 has generally two cotyledons (one in Ceratozamia, and occasionally in other 

 genera also), which are hypogean, 

 remaining in the seed. 



The Cycadacese, of which there 

 are nine genera, and about seventy- 

 five species, are all tropical or sub- 

 tropical. Cycas is a native of the 

 East Indies and Australia ; Macro- 

 zamia and Bowenia, of Australia ; 

 Encephalartos and Stangeria, of 

 Africa ; Zamia, Ceratozamia, Dio- 

 on, and Microcycas, of tropical 

 America. 



Cycas is clearly distinguished 

 from the other genera by its pe- 

 culiar macrosporophylls, involving 

 the absence of a macrosporangiate 

 flower ; Bowenia is characterised 

 by its bi-pinnate leaves ; Stangeria 

 by the pinnate venation of its 

 leaves ; the other genera, by the 

 form of their sporophylls. 



Order 2. Coniferae. This 

 order includes the Pines, Firs, 

 Cypresses, Yews, etc., which, for 

 the most part, are extra-tropical, 

 inhabiting more especially the 

 northern hemisphere. 



The conspicuous features of their morphology are the regular monopodial 

 branching of the stem, the small (often acicular) simple leaves, and the tap- 

 root. In their histology, these plants resemble the Dicotyledons in that the 

 ptem grows in thickness by a normal cambium-ring ; but the vascular tissue of 

 the wood consists entirely of tracheides with bordered pits. The presence of 

 resin-ducts is another characteristic feature. 



The flowers are always monosporangiate ; some genera are dioecious. The 



FIG. 303. Sporophylls of Cycads. A macrc- 

 sporophyll of Cycas revoluta (i nat. size) : f 

 pinnae ; s ovules. JB Macrosporopbyll of Zamia 

 muricata, with two ovules (s) ; C microsporophyll 

 of this species with numerous microsporangia 

 (P). 



