HEPATIC AH 159 



portion, or venter. The lowermost cell of this ventral portion, now 

 known as the ce?ifral cell^ increases considerably in size, and divides 

 by a transverse septum into a lower and larger portion, which encloses 

 the oosphere, and an upper and smaller portion, the ventral ca?ial-ceIL 

 In the meantime the upper layer of cells increases in length by the 

 formation of a number of fresh cells, the neck-canal-cells. The ventral 

 portion of the archegone becomes eventually enclosed in a wall, and by 

 the deliquescence of the neck-canal-cells an open channel is formed 

 down to the oosphere. In addition to the perichaete, the archegones 

 are frequently surrounded by a circular wall originating as an out- 

 growth of the thallus, and known as the perigyne or involucre. 



The result of the impregnation of the oosphere by one or more 

 antherozoids is the production of the embryo, from which is derived the 

 sporogone, which alone constitutes the sporophyte, or non-sexual genera- 

 tion. It is formed entirely from the ventral portion of the archegone. 

 Its external form and internal structure vary greatly in the different 

 groups : as is also the case with the course of cell-divisions in its forma- 

 tion. Ultimately the wall of the spore-capsule becomes differentiated 

 from the archespore, or layer of tissue which develops into the mother- 

 cells of the spores and elaters when these latter organs are present. 

 There is usually no solid axis or columel. The cells which develop 

 into elaters cease early to divide transversely, and thus remain long, 

 while the rest of the cells round themselves off, and become mother-cells 

 of spores. The mature elaters (fig. 159) have in their wall an elongated 

 single or double spiral band, the twisting and untwisting of which on 

 the absorption and giving off of moisture helps to disseminate the 

 spores. Leclerc du Sablon finds the sporogone of the typical Hepa- 

 ticae to be composed, at a very early stage, of sixty-four cells, each of 

 which subsequently divides into four. These cells now elongate in the 

 direction of the axis of the sporogone, and then become differentiated 

 into two kinds. In the one kind the nucleus undergoes repeated 

 bipartitions, and these give rise to the spore-mother-cells ; in the other 

 kind the nucleus does not divide, and the protoplasm forms spiral 

 granulations ; these become the elaters. Rarely (as in Riella) they are 

 replaced by barren cells filled with food-material for the nutrition of 

 the growing spores. The two kinds of cell are equal in number, each 

 alternating with the other. The degree of complexity of the sporogone 

 in the different orders of Hepaticae corresponds in the main to the degree 

 of development of the vegetative organs. In the Jungermanniaceae it 

 bursts longitudinally into four valves, and the walls are composed of two 

 lavers of cells furnished with 'ornaments,' or elevated markings of various 

 patterns ; in the Anthoceroteas it splits longitudinally into two valves ; 



