126 



ELEMENTARY STUDIES IN BOTANY 



of a pine (or to a flower in higher plants) it is often called 

 " fertilization/' but it is evident that it is not. Pollination 

 is a performance that must precede fertilization, and it may 

 or may not be followed by fertilization, which is the fusion 

 of a sperm and an egg. 



75. The embryo. The fertilized egg, lying within the 

 ovule, begins to germinate almost at once, and as the young 



sporophyte (embryo) 

 grows, it feeds upon the 

 surrounding cells of the 

 female gametophyte, and 

 finally reaches a stage 

 in which the different 

 parts become distinguish- 

 able (Fig. 100, A). In 

 the pine, the three re- 

 gions are a stem-like part 

 (hypocotyl) whose tip is 

 directed towards the top 

 of the nucellus (which 

 means that it is directed 



towards the micropyle) J 



a rosette of leaf-like 

 parts (cotyledons) ; and in 

 the midst of the rosette 



of cotyledons, and resting on the top of the hypocotyl, 

 a minute bud-like part (plumule). The hypocotyl will later 

 develop the root, the plumule will develop the stem and 

 leaves, and the cotyledons will for a short time supply 

 nourishment to the young plant. 



Although the fertilized egg germinates almost at once, and 

 the embryo grows until the three regions described appear, 

 it does not continue to grow without interruption, but passes 

 into what is called the dormant (" sleeping ") stage, and the 

 dormant embryo is one of the peculiarities of Seed-plants. 



FIG. 100. A, section of a pine seed, showing 

 the hard coat (testa), the female gameto- 

 phyte (dotted) which has grown to the testa 

 and is usually called endosperm, and the 

 embryo (also sectioned) with its hypocotyl, 

 its cotyledons (three only are shown), and 

 the plumule (the short protuberance) sur- 

 rounded by the cotyledons ; B and C, ger- 

 mination of the pine seed, the cotyledons 

 backing out of the testa in B and entirely 

 free in C. 



