78 BOTANY AND PHARMACOGNOSY. 



tube pushes its way down into the venter, where it discharges 

 one of the sperm nuclei which unites with the egg, forming an 

 oospore. Cessation in growth does not yet take place and the 

 oospore develops into the embryo already described. The develop- 

 ing embryo obtains its nourishment by means of a suspensor 

 (Fig. 50, s), which also places the embryo in a favorable position. 



There being several archegonia in an ovule (Figs. 49, 50), a 

 corresponding number of embryos may be formed, but rarely 

 more than one survives. While the embryo is developing, the 

 other tissues of the megaspore are likewise undergoing changes 

 leading to the maturity of the seed. The carpels and seminifer- 

 ous scales also continue to grow, and they usually become more or 

 less woody, forming the characteristic cones of the pines (Fig. 

 51), but may coalesce and become fleshy, producing the berry-like 

 fruits of Juniper (Fig. 52). The seed on germination gives rise 

 to the sporophyte (tree). 



Groups of Gymnosperms. There are two principal groups 

 of Gymnosperms, (i) one of which includes the Cycads or Fern 

 Palms, which are characteristic of tropical and sub-tropical coun- 

 tries. The trunk does not branch as in the ordinary evergreens, 

 and the leaves form a crown at the summit of the stem or trunk. 

 An important character of some of the Cycads is the production 

 of multiciliate sperms, as in the ferns. Equisetum and Isoetes. 

 (2) To the Coniferge belong the pines, hemlocks, balsams, arbor 

 vitse, junipers (Fig. 51) and cedars, this being by far the largest 

 group of Gymnosperms. 



Exonomic Uses of the Coniferas. From an economic 

 point of view the Coniferse are by far the most important group 

 of plants thus far considered. In fact they may be ranked first 

 in the production of valuable timber. Of those yielding timber 

 the following species may be mentioned: White pine (Piiiits stro- 

 bus) ; long-leaved, yellow, or Georgia pine {Pinus palustris 

 Mill.) ; spruce pine (Pinus cchinata) ; the Redwood of Upper 

 CaHfornia [Sequoia seripervirens) ; pitch pine of New Mexico 

 (Pinus Pondcrosa) ; the Scotch fir. the common pine of Europe 

 (Pinus sylvcstris) . Some of the woods are adapted for special 

 purposes : as that of Pinus Ceinbra of the high mountains of 

 Europe and Northern Siberia, which is excellent for wood-carv- 



