166 



GENERAL BOTANY 



- Roots - 



Fio. 87. Seedlings of the 

 mandrake 



Redrawn from Holm 



Cotyledon 

 -Hypocotyl 



cell. This union of the male and female gametes constitutes the 

 real act of fertilization. The nucleus of the second male gamete 

 unites with one or both polar nuclei ; at least, this is what hap- 

 pens in a large number of instances 

 which have been investigated. This 

 second union of a male nucleus with 

 the polar nuclei results in the formation 

 of the food-reserve material, called the 

 endosperm, which is developed for the 

 purpose of nourishing the young embryo 

 plant until it becomes self-supporting. 



Embryo. The development of the 

 zygote into the embryo takes place 

 immediately after fertilization. The de- 

 tails of this process differ in different 

 species of plants and cannot be dis- 

 cussed here for the mandrake. The 

 embryo in the seed (Fig. 86, d) con- 

 sists of a stem, or hypocotyl, two cotyledons, and a plumule. 



The seed. The seed consists of the 

 embryo, the endosperm, and the integu- 

 ments, which become transformed into the 

 hard seed coats of the ripe seed. The seed- 

 lings, which result from the germination 

 of the seed, are illustrated in Fig. 87. 



The fruit. The fruit is the ripened 

 ovary, in which the walls and the pla- 

 centa become fleshy and constitute the 

 edible fruit of the mandrake (Fig. 88). 



The seeds are finally liberated by the decay of the fruit and 

 lie dormant until conditions favorable for germination occur. 



POLLINATION 



Pollination is the term used to designate the transfer of pollen 

 from the anther of a flower to the stigma. In this text, in the dis- 

 cussion pertaining to pollination, the following terms will be used 

 to discriminate between different kinds, or degrees, of pollination. 



Old stigma 



Old ovary 



fedicd of flower 



FIG. 88. Fruit of the 

 mandrake 



