Plant World Continued 



241 



cellular mass is formed. This cellular mass is the gametophyte. (Fig. 

 145.) 



It is from this gametophyte that several (usually four) sunken 

 archegones arise. The completing process of fertilization may now take 

 place. 



After fertilization the gametophyte becomes stored with food and 

 functions as the endosperm. 



The pollen-tube has also resumed its growth by this time and has 



Fig. 144. I. Carpellate cone, carpels, and seed of the Scotch pine 

 (Pinus sylvestris). 



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 

 ™ n mature seed; t, hard seed coat, or testa, developed from the integu- 

 ment of the ovule, n, a membranous seed coat which is the re- 

 mains 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. 



<H„g. II. The staminate cone, stamen, and pollen of the Scotch pine 

 (Pinus sylvestris). 



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 show- 

 ing 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. Col- 

 lected 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). 



