50 MANUAL OF BOTANY 



sometimes occurring only in special forms. There is a sporox^hyte 

 developed after fertilisation of the contents of the female 

 organ, but this is always a very small structure, incapable of 

 great development, and almost at once producing its spores. 



The sexual organs are antheridia and carpogonia or pro- 

 carpia. The antheridia are borne generally in clusters, which 

 are often situated at the end of a filament {fig. 799), but 

 which may be collected into various groups upon the surface 

 when the thallus is flattened. Sometimes they are found in 

 pits or depressions of the surface, something like the conceptacles 

 of Fucus. Each antheridium produces externally a number 

 of special cells in which the male gametes are produced singly. 

 The gamete is a mass of protoplasm, which at first in most cases 

 has no cell-wall, but which secretes one after its liberation 

 from the mother-cell, usually just before it reaches the female 

 organ. The term applied to the male gamete is ijollinoid or 

 si^ennatiuiyi ; it differs from the antherozoids of the former 

 group in not possessing cilia. The poUinoids are discharged 

 from the antheridial cells by the latter opening at their apices. 



Some botanists hold that the structure described above as 

 an antheridium is really a cluster of them, and that the true 

 antheridium is the special cell alluded to. On this hypothesis 

 the antheridia are numerous and unicellular, and give rise each 

 to a single poUinoid. 



The female organ, or carpogonium, is peculiar in that it 

 never produces an oosphere, but its contents remain undifferen- 

 tiated. It is usuallj' a cell with a somewhat swollen base and a 

 long narrow pointed apex. The latter is called the trichogyne 

 (fig. 799 tr), and is the part which is concerned in the act of fertili- 

 sation. The carpogonium proper is usually the terminal cell of a 

 short branch consistmg of three or four modified cells which are 

 sometimes sunk in the thallus. When the carpogonium is matiu'e 

 a pollinoid comes into contact with the trichogyne, which always 

 projects above the siu-face of the thallus, even if the whole 

 carpogonial branch is not exposed. The wall of the pollinoid and 

 that of the trichogyne become absorbed at the point of contact, 

 and the contents of the former pass into the cavity of the latter. 

 The further stages of the process have not been observed, but as 

 there is no differentiated oosphere it is probable that the 

 nucleus of the poUinoid fuses with that of the carpogonial cell. 

 The trichogyne becomes cut off from the rest of the carpogonium 

 and withers away. 



Fertilisation having been thus accomplished, the further deve- 



