5-1 KintriLizATioN AND i''iairr-KouM\TioN m cuvrronAMS 



tvsi'npod from the I'olls ol" the mothor-plants iuto the aui'TOunding water, and at the 

 time of IVrtili/.atiou they lue destitute of any special coverings of tlieir own. In 

 the plants to be ilcalt with next, on the other hand, the ooplasts at the time of 

 fertilization are still in connection with the mother-plant. The cell-membrano, 

 \\hich maintains this union, persists as an envelope to the protoplasm which is to 

 undergo fertilization. There are two ways in which a fertilizing jirotoplast may 

 exercise its influence upon a protoplasmic body thus inclosed in a cell-niembraue. 

 Either a piece of the envelope is broken through and a free passage made for the 

 spermatoplasm to the ooplasm, or else, if a true fertilization takes place, it must be 

 by osmosis through the en \' elope. 



The solution and removal of part of the cell-membrane enveloping the oopla.st, 

 and the opening up of a passage in which the spermatoplast can unite with the 

 ooplast, is observed to occur in the Mould-fungi known as Mn,coriiil, and also in 

 the innumerable little green and brown water-plants which, on account of their 

 characteristic mode of fertilization, have received the name of Coiijit<jiili.v. In these 

 plants the coalescence of the twai kinds of protoplasts is always preceded by a 

 process of "conjugation", that is to say, the envelopes surrounding those protoplasts 

 come in contact and grow together, and a special cavity is thereby created in which 

 the fusion of the protoplasts can take place. This method of fertilization is shown 

 in the clearest manner in fig. 204 ^■''■'•'■■\ the instance being that of Sporodinia. giviidin, 

 a Fungus belonging to the Mucorini. Two more or less parallel ttibular hyphro put 

 forth lateral protuberances (fig. 204 ^) which stretch out towards one another until 

 their free ends come into contact and cohere. As soon as this union is eiiected, ii 

 transverse wall is I'ormed on either side of the plane of contact, and it is now 

 possible to distinguish in the limb connecting the two hyphte a median pair of cells 

 supported by the two basal portions of the outgrowths (see fig. 204 *). The con- 

 necting limb is usually lilcened to a yoke {tvy6i>). The wall arising from the junction 

 of the outgrowths, and now separating the two cells in the middle of the yoke, 

 dissolves, thus producing a single cell-cavity (instead of the two), which is called a 

 " zygogonium ". The two protoplasts inhabiting the paii- of cells wore hitherto 

 separated, one being derived from the hypha to the right, a.nd the other from the 

 hypha to the loft; they are two diflbrent individuals, but, upon the (lissolution of 

 the wall between them, they coalesce within the zygogonium. This coalescence is 

 to be looked upon as the act of fertilization. The membrane of the median cell, 

 which surrounds the blended mass of protoplasm, thickens, and, in the selected 

 instance of Sporodinia grandis, becomes warted, whilst in Mucor Mvccdo (fig. 

 193') it becomes rough and wrinkled, and in other Mucorini even spinose. It also 

 acquires a decided dark coloration. Lastly, the dark median cell detaches itself 

 from the basal portions of the original outgrowths, which have held it up to that 

 time, and thus becomes free and independent (see fig. 204 ''). It then drops just as 

 a cherry does from the twig of a tree, and, like tlie cherry, it must be dissignntod as 

 a fruit, although it consists of a single cell only, l^'ruits of this kind have I'cceived 

 the name of " zygotes ". 



