no FERNS THE ANCESTORS OF FLOWERS 



and repulsion caused by light is called " phototaxis," that 

 caused by moisture " hygrotaxis," and so on. A most 

 important chapter in our knowledge of the activities of 

 protoplasm and of simple protoplasmic cells is based on 

 the study of these attractions and repulsions, which, whilst 

 they appear as arbitrary properties determined by causes 

 which are not immediately evident, are yet capable of 

 modification by experimental alteration of the conditions 

 in which the protoplasm exists, so that we are entitled to 

 speak of " the education " of such microscopic particles by 

 which they can be rendered either more or, on the other 

 hand, less sensitive to " chemotactic " agents. 



To revert now to the question of the relationship of 

 ferns to higher plants. The following points are of impor- 

 tance : ( I ) Though true ferns produce from their spores 

 prothalli which carry both sperm-sacs and egg-pits on the 

 same specimen, yet some fern-like plants produce prothalli 

 which carry only egg-pits, and others which carry only 

 sperm-sacs, the two kinds growing side by side from the 

 spores shed by the fern; (2) the spores which produce the 

 female or egg-bearing prothalli are in some cases much 

 larger than those which produce the male, or sperm-sac- 

 bearing prothalli. We then distinguish large female-pro- 

 ducing spores from small male-producing spores; (3) some 

 ferns for instance our native Royal fern (Osmunda 

 regalis] do not produce spores on all the leaflets of a 

 frond, but only on those near the tip, which are narrower 

 and less leaf-like than those lower down (Fig. 10, A). 

 Hence this fern is called " the flowering fern." For the 

 essence of a flower is that it is a set of leaves like the 

 other leaves of the flowering plant, usually not green and 

 flat, as they are, but modified one or more whorls of 

 them being often coloured and arranged, so as to close 

 over the terminal or tip leaves, which are called " stamens " 

 and " carpels," and bear the reproductive particles (Fig. i o, 



