COXIFERALES (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 Araiicaria brasiliana by Strasburger 

 (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 functions of the tiers 

 of the proembryo, the lowest tier developing 

 this embryo cap, the middle tier producing 

 the embryo, 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 Cephalotaxiis 

 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, involving 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, two cotyledons appearing quite 

 uniformly in Sciadopitys, Cunninghamia, Sequoia sempervlrens, and 

 Arthrotaxis; two or three in Cryptomeria; and three to six in Sequoia 



Fig. 366. — Taxodium 

 distichum; apparently three 

 embryos in a group uniting 

 to form a single embryo; 

 the embryonal tubes are 

 conspicuous; X180. — After 

 COKER (76). 



