SPERMATOPHYTES 



213 



of the southern hemisphere as are the pines of the northern hemi- 

 sphere. The taxads in general are north temperate, Taxus (yew) being 

 the most widely distributed genus. 



Sporophyte. — The habit of the sporophyte 

 body is familiar, in general being the branching 

 habit established in Ginkgo and common to all 

 conifers. In size the body ranges from large 

 trees to straggling bushes. The mesarch type 

 of bundle, characteristic of ferns, occurs in the 

 stem of at least one species (a Cephalotaxus), 

 but in most of them it is found only in the 

 cotyledons, as in Ginkgo. The leaves are entire, 

 as in all conifers, and range in breadth from 

 the needles of Taxus to the broad blades of 

 certain species of Podocarpus. 



Staminate strobilus. — The staminate strobilus 

 is always a distinct strobilus, enveloped by 

 sterile bracts (as among Cordaitales, fig. 473). 

 The sporophylls differ in form in the two tribes. 

 Among the podocarps the sporophyll is bract- 

 like, with two abaxial sporangia and a sterile 

 tip (fig. 474); while among the taxads the spo- 

 rophyll is peltate (epaulet type), as in Ginkgo, 

 and bears a variable number of pendent spo- 

 rangia (figs. 475, 476). The development of 

 the microsporangium is as usual among euspo- 

 rangiates. The microspores (pollen grains) of 

 the podocarps are peculiar in being winged, 



each pollen grain developing two winglike ex- longitudinal sections of 

 tensions from the exine, as among the pines. young staminate strobilus 



Ovulate strobilus. — The ovulate strobilus is ° . orrc . ya ' s ° W '" R *? 



overlapping bracts (or) and 



much reduced, usually containing a single the position of the develop- 

 terminal ovule. For example, in Torreya in s stamens (a). — After 

 (nearly related to Taxus) the ovulate strobilus 



resembles a simple ovulate flower, with four bracts (two decussate 

 pairs) investing a terminal ovule (fig. 477). 



Ovule. — The integument of the ovule is of the ancient type, develop- 

 ing three distinct layers (outer fleshy, stony, and inner fleshy); and a 

 set of vascular strands traverses the outer fleshy layer, the inner set 



Fig. 473. — Cross and 



