CHAPTER VI. 



THE BIOLOGY OF A PLANT (Continued). 

 THE BRAKE OR FERN. 



Reproduction. The highly important generative function is 

 performed in Pteris by structures which are very unlike and 

 somewhat complicated. The subsequent descriptions of these 

 organs will be better understood if prefaced by a brief account of 

 reproduction in general, as well as in the special case of the fern. 



Living things give rise to offspring by the detachment of cer- 

 tain portions or fragments of their own bodies, endowed with 

 the power to grow and develop into complete individuals ; and 

 so far as known, living things never arise except through this 

 process. The detached portions are sometimes masses of cells 

 (vegetative reproduction), as in the separation of whole branches 

 or of special, so-called adventitious, buds, but more commonly are 

 single cells (like the ova of animals and the spores of ferns and 

 mosses). 



All forms of reproduction fall under one or the other of two 

 heads, viz., Agamogenesis (asexual reproduction) or Gamogenesis 

 (sexual reproduction). In the former case the detached portions 

 have the power to develop into new individuals without the 

 influence of other living matter. In the latter, the detached 

 portion, in this case always a single cell called the germ (ovum, 

 oosphere, etc.), is acted upon by a different portion of living mat- 

 ter, likewise a single cell, which in most cases has been detached 

 from the body of another organism. The germ is called the 

 female germ-cell; the cell acting upon it the male germ-cell; 

 and in the sexual process the two fuse together (fertilisation, 

 impregnation} to form a single cell endowed with the power of 

 developing into a new individual. In some organisms (e.g., the 

 yeast-plant) only agamogenesis has been observed; in others (e.g., 

 vertebrates) only gamogenesis. In still others, both processes take 

 place, and of such organisms the fern is a conspicuous example. 



