EMBRYOGENY IN CELLULAR PLANTS. 267 



one cell, considered as the male, pass into the other in which the spore 

 is produced, as in Zygnema (fig. 471), and sometimes the contents 

 of both cells unite, and the spore is produced in the tube between 

 them. Besides this process of conju- 

 gation, by means of which a cellular 

 embryo is formed, some of these plants 

 have a power of merismatic or fissi- 

 parous division (fig. 472), by which 

 cells are separated, capable of inde- 

 pendent existence. This may be 

 compared to the process of budding, Kg. 472. 



and is thus distinct from fecundation. 



In many of the Confervse, however, spores appear to be produced 

 without the conjugation of separate filaments. In such instances it 

 is conjectured that different cells in the same filament perform different 

 functions, and are so placed that at a certain period their contents by 

 coming into contact develop a fertile germ. The same filament may 

 thus contain both- male and female cells ; although botanists as yet 

 have not been able to show the difference between them. In some 

 species of Meloseira the endochrome at each end of the cell appears 

 to have a different property, and mixture takes place in the cavity 

 of a single frustule. In this case there is a movement towards the 

 centre of the cell where the spore is formed. 



Proceeding to other divisions of Acotyledons, we find different 

 kinds of reproductive organs, which can, however, only be observed 

 at certain periods of development, and frequently cannot be seen after 

 the embryo has been fully formed. In the same way as in flowering 

 plants, when the seed has been ripened the stamens have generally 

 withered and fallen off, and sometimes also the style and stigma. It 

 is of importance, therefore, in all investigations into Cryptogamic 

 reproduction, to examine the plants at an early period of their growth. 

 The reproductive organs have received different names in the several 

 orders of Cryptogams. The usual name applied to the male organs 

 is antheridia, containing sperm-cells with phytozoa ; and to the female 

 organs, archegonia, containing germ-cells. 



We shall now proceed to examine the reproductive organs and 

 their functions in various divisions of flowerless or Cryptogamous plants. 



In the case of Fungi (the mushroom order), reproductive bodies 

 called spores are produced, either naked (often stalked) or contained in 

 sacs called thecce (6rixri, a box) or asci (asms, a bag). Many of the 

 spores, such as those called conidia (xovig, dust), are rather of the nature 

 of buds. In some fungi, as Peronospora, a conjugation of cells has been 



Fig. 472. Diatomaceous Alga (Diatcnna TnariTvwm), the cells of wMcli are increased by a 

 constant process of fissiparous or merismatic division. The plant increases by abscission 

 of segments. 



