242 



GENERAL BIOLOGY 



the supply of water becomes less and less the cone becomes dry and 

 consequently the young sporophyte stops growing. The cone and seeds 

 are now said to be ripe, so that as the dry seed scales are spread out and 

 blown away the part of the seed which contains the embryo is carried 

 with them, and as soon as water is again supplied the embryo again 

 begins to grow, breaking the brittle integument or indusium covering it, 

 and the root is ready to penetrate the soil and carry water to stem and 

 leaves of the new plant. 



FLOWERS 



The flowers of flowering plants (Fig. 146) consist of cone-like clus- 

 ters of closed megasporophyls (carpels) above, and microsporophyls 



(stamens) below, subtended 

 by a perianth. The plant on 

 which the flowers grow is the 

 sporophyte. 



The microspores or pol- 

 len-cells (Fig. 147) each pro- 

 duce a mature gametophyte 

 which consists of a pollen tube 

 with three nuclei (Fig. 148 B) ; 

 one, the nucleus of the pollen 

 tube itself, and the other two 

 sperm nuclei. 



The megaspore is retained 

 within the ovule (Fig. 148 A), 

 (megasporangium). A gameto- 

 phyte with a single egg devel- 

 ops within the ovule. After 

 fertilization, the zygote devel- 

 ops into an embryo and an en- 

 dosperm, to be described 

 shortly, while the entire ovule 

 becomes covered with one or 

 two coats to form the seed. 

 With proper moisture and soil, 

 the sporophyte escapes from 

 the seed as with the pine. (Fig. 



ciples of Botany," by permission of Ginn & Co. Pub- 1/1Q \ 

 lishers). 4 ^0 



The purpose of a flower is the production of seed. The ripened 

 carpel with its contained seed is known as a fruit. (Fig. 150.) 



The Buttercup (Fig. 151) will serve as an excellent example of the 

 flowering plants. Here we have many carpels (simple pistils) each 

 made up of an ovary (the simple closed cavity below) which gradually 

 tapers to a soft terminal stigma. The carpels are flat and open when 



pe \~ 



Fig. 146. Floral Organs. 



A, Orange blossom. (After Bailey). 



B, Hydrophyttum, col, lobe of calyx ; cor, lobe of 

 corolla; st, stamens; p, pistil. (After Lindley). 



C, Diagrams of flower, showing face-view and 

 dissection, r, receptacle ; se, sepal ; pe, petal ; st, 

 stamen ; pi, pistil ; o, ovule. 



The parts of a complete bisexual flower of the 

 higher seed plants (angiosperms) are sepals, petals, 

 stamens, and pistils. The sepals, taken together, 

 constitute the calyx ; the petals, taken together, con- 

 stiute the corolla. The calyx and corolla are col- 

 lectively known as the floral envelopes, or perianth. 



Many angiospermous flowers consist of five cir- 

 cles, or whorls, two of which belong to the perianth, 

 two to the stamens, and one to the pistils. The parts 

 of each circle alternate in position with those of the 

 preceding or following one, and all the members of 

 each circle are alike. (From Bergen & Davis "Prin- 



