174 MANUAL OF BOTANY 



DIVISION A.—GYMNOSPEBM^. 

 Class IX.— GYMNOSPEKMiE. 



The plants included in tins class are distinguished by their 

 niacrosporophylls never forming an ovary, the carpels being 

 usually flattened and bearing the macrosporangia on their upper 

 surfaces. In habit they are shrubs or trees, generally of consider- 

 able size. In our climate they are chiefly represented by the 

 Coniferous trees. Firs, Larches, &c., which have a monopodially 

 branched stem, bearing usually long branches, on which dwarf 

 shoots are thickly placed, the latter consisting of small fascicles 

 of two to several elongated green leaves springing from a short 

 axis and surrounded at their base by minute withered or brown 

 scales. The long branches bear no foliage leaves except Avhat 

 arise from tlieir dwarf shoots. 



The stem in other members of the group is a short thick 

 trunk, bearing large pinnate leaves ; in Welwitscliia it is very 

 short and bears onl}- two leaves, which are very long. 



A few form.s have a bushy habit, with wir}' stems which 

 bear no foliage leaves, but only a number of scales. 



The sporangia are of two kinds, as already stated. The micro- 

 sporophylls are usually' collected into cones, and bear the 

 sporangia on their lower surfaces. The macrosporangia are 

 axial in Taxus and in the Gnetaccce ; in the other cases they are 

 borne on sporophylls. These, like the microsporophylls, are 

 generally arranged in cones, but the sporangia are on the upper 

 surface at the base of the sporophyll, sometimes upon a large 

 placental scale. In Cycas the sporophyll is a pinnate leaf, the 

 lower pinna; of which are replaced by macrosporangia. A cluster 

 of these sporophylls is developed at the apex of the stem among 

 the foliage leaves. 



The development of the sporangia and of the spores has 

 already been described. 



A few features of the histology are remarkable. The stem 

 is of the same type as the Dicotyledons, but is peculiar in that 

 the wood formed by the cambium, except in th§ Gnetacese, always 

 consists of fusiform tracheids with bordered pits upon their 

 radial walls. The sieve tubes, like those of the Pteridophyta, 

 have no companion cells. There is a great development of 



