Gymnospermous Plants — Conifers and Their Allies 203 



(Gr. kotyle, cup or vase). The embryo is surrounded by the endosperm 

 (food) which is covered by the seed coat (hardened integument). The 

 seed thus formed was originally the ovule and contains a wing for wind 

 dispersal. When a seed germinates, the embryo produces a young seed- 

 ling which eventually develops into a pine tree (sporophyte generation). 

 Since gymnosperms produce two different kinds of spores (microspores 

 and megaspores), they are heterosporous. 



Conifers are of great economic value, serving as sources of lumber for 

 furniture, buildings, boxes, poles, railroad ties, etc., wood pulp for the 

 manufacture of paper, and numerous other uses. Cedars and their allies 

 are used in making shingles, pencils, cedar chests, etc. The balsam fir 

 produces a resin from which Canada balsam is manufactured. The lat- 

 ter is used to affix coverglasses on slides permanently. Certain types of 

 pines yield turpentine, rosin, pitch, and similar products. 



CYC ADS (SAGO PALMS) 



Zamia (za' mi a) (L. zamia, fir cone). — The cycads (sago palms) be- 

 long to the class Gymnospermae and the order Cycadales (sik a -da' lez) 

 (Gr. kykas, coco palm). They are palmlike trees or low shrubs with 

 unbranched stems, terminating in a tuft of thick, pinnate (fernlike) 

 leaves which are often spiny edged. In Zamia (Fig. 54), which occurs 

 in Florida, the short, tuberous stem is not over four feet tall and bears 

 a crown of leathery, pinnate leaves. Sometimes much of the stem is 

 underground. In general, the cycads are inhabitants of the tropics or 

 semitropics. 



Zamia is diecious since male and female cones are borne on separate 

 plants. The female carpellate cones are composed of peltate (shield- 

 shaped) megasporophylls, each of which bears two ovules, with a micro- 

 pyle (small opening) in the enclosing iyitegument. In the center of the 

 ovule is the megasporangium (nucellus) . The latter contains one mega- 

 spore mother cell which produces four megaspores, three of which dis- 

 integrate. The nucleus of the remaining megaspore divides to form two 

 nuclei, and further division results in numerous nuclei. Walls separate 

 the nuclei, so this multicellular tissue becomes the female megagameto- 

 phyte which produces two to six archegonia. Each archegonium consists 

 of one large egg and a iieck. 



The male staminate cones are smaller than the female and consist of 

 numerous micros porophylls. Each of the latter bears numerous (thirty 

 to forty) microsporangia on the lower surface. Each microsporangium 



