GROUP IV. GYMNOSPEBM.E. 431 



The fruit-cone, in most cases, sets free the seed by the separa- 

 tion of the macrosporophylls, or of the placeutal scales, which fall 

 off from the axis of the cone, leaving it bare (most Cycadaceae, also 

 Abies, Cedrus) ; or they merely separate enough to let the seeds 

 fall out, and then the cones either remain on the tree (e.g. Larix), 

 or, as is more commonly the case, drop off entire. However, where 

 the fruit is a berry-like cone (e.g. Juniperus), the macrosporophylls 

 do not separate, and the dispersal of the seed depends on the fruit 

 being eaten by animals. 



2. The seed is albuminous in all Gymnosperms, the single 

 straight embryo being imbedded in the endosperm (see Fig. 251 /) 

 in all cases, also, some portion of the nucellar tissue persists as 

 perisperm, amounting, in the Cycadaceae and Coniferae, to little 

 more than a membranous layer. 



The development of the seed-coats varies widely. In the 

 Cycadacese the testa consists of two layers, an outer fleshy and 

 succulent, and an inner hard and woody, so that the seed bears a 

 superficial resemblance to a fruit such as a plum. In those Coni- 

 ferae in which the seeds are produced in a cone-fruit, the testa is 

 hard and tough ; but in those in which the seed is exposed from 

 the first, the testa is either fleshy (e.g. Ginkgo, Cephalotaxus), 

 being developed after the manner of that in the Cycadaceae, or it 

 is hard, and is invested by a succulent aril (e.g. Taxus). In those 

 Coniferae with woody cones (e.g. Abietineae, most Cupressineae) 

 the seed is usually winged, either by means of a membranous 

 outgrowth of the testa, or (Abietineae) by the adhesion to the seed 

 of a thin strip of tissue, split off from the surface of the placental 

 scale. 



Classification of the Gymnospermce. 



The group contains the following three orders : 



1. CYCADACE.E: the trunk is generally un branched : the leaves 

 are large and branched : no vessels in the secondary wood. 



2. CONIFERAE : trunk much branched : leaves many, small, and 

 unbranched : no vessels in the secondary wood. 



3. GrXETACE^E : habit various : flowers have a rudimentary 

 perianth : there are vessels in the secondary wood. 



Order 1. Cycadaceae. The CycadacesB are plants which, in many re- 

 spects, show affinity with the Ferns, while, on the other hand, they re- 

 semble the Palms in external appearance. The stem is tubercular or 

 cylindrical. The vegetative leaves are of two kinds ; scaly leaves, brown 

 and dry, closely covering the surface of the stem ; foliage- leaves, pinnate, 



