GERMINATION 523 



circumnutating and emerging in the form of an arch, owing to 

 the greater growth of one side. After reaching the air the 

 region of greatest growth changes to the opposite side and the 

 epicotyl straightens itself. During this time it subsists upon 

 the nourishment stored in the cotyledons. This is called hypogean 

 germination. In the other method, that of the so-called epigean 

 germination, the cotyledons rise above the ground and become 

 green, the hypocotyl behaving as did the epicotyl in the first 

 ease. These are generally, though not always, albuminous 

 seeds, and the nutritive matter is stored outside the embryo. 

 In both cases the root makes its way. into the soil by virtue 

 of its geotropism and apheliotropism, aided by the movement 

 of circumnutation, and by the adhesion of the root-hairs to 

 particles of the soil. In Monocotyledons the upper part of the 

 single cotyledon generally remains in the seed and absorbs the 

 nutriment from the endosperm, while its base elongates and 

 thrusts the young plant downwards. 



Sometimes the usual alternation of sexual and asexual re- 

 production in the higher plants is interfered with by the sub- 

 stitution of the vegetative method for one of them. In the 

 ' phenomenon of apospory noticeable in some Ferns we have 

 small prothallia developed on the back of the leaves in the place 

 of spores. This is a case of the production of a bud instead of 

 an asexual cell. Conversely, among the same group of plants, 

 the sporophyte sometimes arises as a bud or vegetative outgrowth 

 upon the prothaUium, a phenomenon known as apogamy. 



There is another kind of apogamy known which is generally 

 ienxiQdi parthenogenesis. This occurs among the Fungi, where, 

 as in Saprolegnia, oospheres are formed in oogonia, which do 

 not become fertilised and yet have the power of growing out 

 into new plants. The formation of azygospores, described as 

 occurring in Mucor and other plants, is another case of the same 

 phenomenon. This parthenogenesis differs from the phenomenon 

 described as occurring in Ooelehogyne, where nevertheless an 

 embryo is produced without pollination. This we have seen to 

 be due to a vegetative budding of the cells of the nucellus of 

 the ovule, the buds growing into the macrospcre and there de- 

 veloping into embryos. 



