178 



PHYSIOLOGICAL BOTANY. 



In the case of the CONIFERS (Pines, Cedars, Mrs), where no styles or stig- 

 mas exist, the pollen falls directly into the microphyle of the naked ovule, 

 and its tubes settle into the tissue of the nucleus. 



438. Germination. The ovule matures with the 

 completion of the embryo, and passes into the fixed 

 state of the seed in which the embryo 



sleeps. A store of nutritive matter, 

 starch, gluten, etc., is thoughtfully pro- 

 vided in the seed for the use of the 

 young plant in germination, until its 

 root has gained fast 

 hold of the soil. 



439. The changes 

 which occur in the 

 seed at the recom- 

 mencement of growth 

 are simply such as are 

 requisite to reduce its 

 dry deposits to a solu- 

 tion which shall 



the proper 



/? II C rkT , TVI Q Tne fertilized cell has divided itself into several, of which c, b 



-IOI ina- constitute the suspensor attached te the apex of the sac ; a, em- 



tion or growth. Gluten b 



and other nitrogenous matters, oil, starch, etc., are to 

 be changed to diastase and dextrine. To accomplish 

 this, water is taken up, oxygen absorbed, plant-food 

 dissolved and moved to points where it is needed, and 

 used in constructing new cells and tissues. 



440. Ripening of Fruits. After the fruit has attained its full growth 

 the process of ripening commences, during which the pulp becomes gradually 

 sweetened and softened, chiefly by the change of the starch into more or less 

 of soluble sugar. Thus ripening is to the pericarp what germination is to the 

 seed. In its earliest stage the pericarp consists of structure similar to that of 

 green leaves, composed of cellular, vascular, and woody tissues, and epider- 

 mis and stomata. Its distended growth afterward results from the accumula- 

 tion of the flowing sap, which here finds an axis incapable of extension. Thus 



530, Ovule of Viola tricolor, showing the process of fertili- 

 zation; p, pollen; t, tube; r, raphe; c, chalaza; 6, primine; a, 

 secundine; n, nucleus; s, sac, which the tube appears to have 

 Illdf penetrated. 531, Growth of the embryo in Hippuris vulgaris. 



