1 66 Practical Plant Biology. 



and of the ventral canal-cell open a way down to the ovum which 

 lies in the body or venter of the archegonium. 



The same supply of water which brings about the ejection and 

 maturation of the sperms will probably open the necks of several 

 archegonia. As in the case of Marchantia and Funaria the sperms 

 are guided chemotactically to the ova. In this case it has been 

 found that malic or maleic acid acts as an attractive substance. 

 Hence it is probable that either of these organic acids is developed 

 in the disintegration of the neck and ventral canal-cells. 



The sperms swarm round the lately opened necks and crowd 

 down into their canals. One only as far as has been observed 

 enters into the ovum and its nucleus fuses with the nucleus of the 

 ovum. Before fusion the two nuclei are very different in appear- 

 ance. The sperm-nucleus is a spiral band or ribbon of apparently 

 homogeneous protein giving the reaction of nucleic acid and con- 

 stituting the chromatin. The nucleus of the ovum, on the other 

 hand, has its chromatin, or protein giving the nucleic acid reaction, 

 distributed in very fine granules arranged along threads forming a 

 fine net-work suspended in the fluid of the nuclear vacuole. One 

 or more rounded bodies, the nucleoli, are also found floating in this 

 nuclear fluid. In fusion the chromatin of the sperm passes right 

 into the nuclear vacuole of the ovum and becomes mingled with the 

 chromatin of the ovum. This fusion constitutes fertilisation. The 

 difference in size of the two gametes and of their two nuclei should 

 be noted. But it should also be observed there is not the same 

 disparity between the masses of chromatin contributed to the 

 oosperm by the two gametes. 



Immediately after fertilisation the oosperm becomes coated over 

 with a cell-wall. It then divides and becomes a spherical mass of 

 cells. This mass grows rapidly in size and soon bursts the arche- 

 gonium. Part of it pushes out as a root and grows downwards into 

 the soil, while from the opposite hemisphere, which is turned 

 towards the growing region in the indentation of the parent gameto- 

 phyte, a first leaf and stem are developed. During the early stages 

 of the growth of these organs, the new plant retains connection with 

 the gametophyte by means of a short, suctorial organ and derives 

 food from it. This organ is called the foot, and is developed from 

 the same hemisphere of the oosperm as the first root. The first 

 leaf soon turns upward, usually through the indentation in the 

 gametophyte, and expands a single leaflet resembling those of the 

 fern-plant in appearance, and having also their opaque green colour 

 unlike the transparent green of the gametophyte. During the de- 

 velopment of these organs the nutrition of the young plant is supplied 



