. Morphology of gymnosperms. Gymnosperms; Plant morphology. CONIFERALES (PINACEAE) 297 the earliest divisions and the beginning of the vascular system of the seedling there is a hiatus in our knowledge. The only information in reference to the embryo of the Araucari- neae is an early account of Araucaria brasUiana by Strasbtjrger (25) (figs. 367, 368). The stem tip is not terminal, but is covered by a small group or layer of cells which is soon thrown off, and seems for a time to serve as an organ of penetra- tion or protection. This terminal group of cells shifts the usual fimctions of the ti
. Morphology of gymnosperms. Gymnosperms; Plant morphology. CONIFERALES (PINACEAE) 297 the earliest divisions and the beginning of the vascular system of the seedling there is a hiatus in our knowledge. The only information in reference to the embryo of the Araucari- neae is an early account of Araucaria brasUiana by Strasbtjrger (25) (figs. 367, 368). The stem tip is not terminal, but is covered by a small group or layer of cells which is soon thrown off, and seems for a time to serve as an organ of penetra- tion or protection. This terminal group of cells shifts the usual fimctions of the tiers of the proembryo, the lowest tier developing this embryo cap, the middle tier producing the embrj'o, the tier next above (ordinarily the rosette) forming the suspensor. It is an interesting fact that this same feature is found also in the embryo of Cephalotaxus Fortunei (25) (figs. 369, 370). The origin of the testa is but little known in detail, but the region of its development may be seen in fig. 275. Next to the endo- sperm is a dry, membranous layer derived from fleshy tissue; outside this is the hard layer, which in the upper region, at least, comes from the middle layer of the integu- ment; the outermost layer, dry and incom- plete, comes from fleshy tissue (fig. 371). The number of cotyledons among Pina- ceae, invohing as it does the origin of polycotyledony, is an interesting and im- portant topic. The Bennettitales, Cycadales, and Ginkgoales have given the impression that the primitive number of cotyledons is two, but this still remains an open question. Among the Pinaceae the number varies from two to fifteen, and the fluctuations hold no relation to the tribes, except that the higher numbers are characteristic of the Abie- tineae, in which the recorded range is three to fifteen. Among the Taxodineae the range is two to six, tno cotyledons appearing quite uniformly in Sciadopitys, Cunningkamia, Sequoia sempervirens, and Arthroiaxis; two or three in Cryptomeria; a
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