240 



GENERAL BIOLOGY 



After fertilization the gametophyte becomes stored with food and 

 functions as the endosperm. HI 



The pollen-tube 

 has also resumed its 

 growth by this time 

 and has brought the 

 two non - ciliated 

 sperm to the mouth 

 of an archegone. One 

 of the . sperm fuses 

 with the egg which 

 completes fertiliza- 

 tion. This fertiliza- 



tion takes place in 

 the pines more than 

 a year after pollina- 

 tion. 



The fertilized 

 egg, now called a 

 zygote, gives rise to 

 the embryo consist- 

 ing of a cylindrical 

 stem with narrow 

 whorled leaves and a 



Fig. 144. I. Carpellate cone, carpels, and seed of the Sco^cn pine (Firms sylveatris) . 



A, young growth with carpellate cones, about three weeks after the opening of 

 the terminal bud : n, young pine needles. B, inner and side view of a cone scale 

 at the time of pollination as shown in A : b, bract ; o, ovules. C, inner and side 

 view of scales from a mature cone as shown in D : b, bract ; o, fertilized ovules 

 now rapidly maturing into winged seeds ; w, the developing wings. D, a. mature 

 cone. E, a mature winged seed. F, section of mature seed ; t, hard seed coat, 

 or testa, developed from the integument of the ovule, n, a membranous seed coat 

 which is the remains of the nucellus ; en, endosperm or tissue of the female 

 gametophyte ; em, embryo with group of cotyledons c and the suspensor s ; m, 

 micropylar end of seed. 

 II. The staminate cone, stamen, and pollen of the Scotch pine (Pinus sylvestria ) . 



A, young growth, with staminate cones about two weeks after the opening of 

 the terminal bud. B, details of cone. C, end view of stamen. D, side view of 

 stamen. E, pollen mother cell developing four pollen grains in a tetrad. F, pollen 

 grain showing the two wings ; p, prothallial cell ; g, generative cell ; t, tube 

 nucleus. E, (After Miss Ferguson). 



III. White pine. 



(Pinus Strobus) . Longitudinal section through an archegonium at the time of 

 fertilization. Above the fusing nuclei are various other elements emptied into the egg 

 from the pollen-tube. Collected June 21, 1898. X about 62. s.g., starch grains ; p.r., 

 prothallium ; c.p.t, cytoplasm from pollen-tube ; st.c., stalk-cell ; t.n, tube-nucleus ; 

 s.n, sperm-nucleus; e.n, egg-nucleus; n.s, nutritive spheres. (After Margaret C. 

 Ferguson). I, II, (From Bergen & Davis "Principles of Botany," by permission 

 of Ginn & Co. Publishers). Ill, (From C. Stuart Gager's "Fundamentals of 

 Botany," by permission of P. Blakiston's Son & Co. Publishers). 



