GROUP IV. GYMNOSPERM^E. 



437 



not cones ; the seed usually projects beyond the macrosporophylls (when 

 present) and has a succulent testa or an arillus: flowers generally 

 dioecious. 



Fam. 1. Taxece : the macrosporophylls are usually rudimentary or 

 absent, and the macrosporangia are borne on the axis : the seed has an 

 arillus in some forms, while in others it has a succulent testa : micro- 

 sporophylls with 2-9 microsporangia : microspores without expansions of 

 the exine. 



PhyllocJadus, remarkable for its rudimentary leaves and for the de- 

 velopment of its dwarf-shoots into phylloclades, has thick persistent 

 macrosporophylls ; in the axil of each there is a single erect macrosporan- 

 gium with an arillus : flowers sometimes monoecious. Ginkgo Uloba (Salis- 

 buria adiantifolia), the Maiden-hair Tree, is characterised by its fan- 

 shaped deciduous leaves with furcate venation : the macrosporophylls are 

 rudimentary: the macrosporangia are borne in an opposite pair at the end 

 of a short stalk : no arillus, bat the testa of the seed becomes succulent. 

 Taxus(the Yew) has only long shoots: nor has this genus any macro- 

 sporophylls, the macrosporangia 

 being borne singly at the end 

 of short lateral shoots, and the 

 seed has a fleshy arillus : there 

 are no resin-ducts in the tissues : 

 the microsporophyll is peltate, 

 bearing 5-9 microsporangia on 

 its under surface. 



Order 3. Gnetaceae. This 

 order includes but three genera, 

 Ephedra, Gnetum, and Wel- 

 witschia. Though they differ 

 widely from each other in many 

 respects, they agree in that they 

 have opposite leaves ; flowers 

 which are not cones and which 

 have a rudimentary perianth, 

 but have no macrosporophylls 

 as the macrosporangia are borne on the axis : an albuminous erect seed ; 

 a dicotyledonous embryo ; and secondary wood which contains true 

 vessels. They are generally dioecious. 



Ephedra is a genus of shrubby plants, with rudimentary leaves, some- 

 what resembling an Equisetum. It is especially remarkable on account 

 of its peculiar embryogeny. Habitat, warmer temperate zone. 



Gnetum is a genus of shrubs or trees, for the most part climbers, but 

 some erect-growing (Gnetum Gnemori) : with its broad well-developed foli- 

 age-leaves, with pinnate venation, it resembles the Dicotyledons in habit. 

 Habitat, the tropics. 



Welwitschia includes the single species W. mirabilis .- it is remarkable 

 for its short thick stem, prolonged below into a tap-root, with a broad flat 

 somewhat circular bilobed upper surface, a single long persistent foliage- 



FIG. 258. A Branch of Taxus baccaia bearing 

 a fruit/, which consist* of a fleshy arillns en- 

 closing a seed. B Longitudinal section of the 

 end of a branch terminating in a macrospo- 

 rangiate flower: b scaly bracts; fc terminal 

 macrosporansrium(nucellu8); v the integument; 

 m the micropyle : a the rudiment of the arillns 

 (X20). 



