3i8 STUDIES IN LIFE AND SENSE. 



be understood how rigidly plant-habits must mould the life of the 

 vegetable world, with the stable force of gravitation serving as an all- 

 important condition in the formation and continuance of these habits. 

 We shall presently observe that the influence of light on the growing 

 plant is to be regarded as a second factor of importance in the form- 

 ation of the habits of the plant-universe. 



But it might be urged that the fixation and rigidity of the habits 

 in question should preclude the plant from participating in those 

 modifying circumstances to which the worlds of life are now univer- 

 sally regarded as subject. If variation and change, as factors in pro- 

 ducing new species, are to be regarded as operating influentially 

 within the plant-domain, it must be shown that the instincts of the 

 plant should be capable of being affected by alterations of its envi- 

 ronment and surroundings. Such an expectation is amply fulfilled by 

 the result of botanical research. We know that it is the habit 

 of the plant-root to grow downwards in obedience to gravity, as, con- 

 trariwise, by the greater growth of the under side of the, at first, hori- 

 zontal stem, its point is forced upwards and from the earth towards 

 the light. But these natural habits may be interfered with and altered, 

 as already remarked. If seeds be placed amongst damp sawdust in 

 a perforated and suspended zinc frame, they at first obey the law 

 of habit which compels them to grow downwards into the air, as if 

 seeking their native earth. But the dry air presents less attraction 

 for the young roots than the moist sawdust. Starvation awaits them 

 below, whilst they have just grown through a land of plenty, as re- 

 presented by the moist sawdust of the frame. Hence, an instinct 

 which may appropriately enough be termed that of self-preservation 

 influences the rootlets ; and instead of continuing their profitless 

 downward increase, they return to the moist sawdust above. The 

 mere structural explanation of these movements, as connected with 

 greater growth above or below on root and stem, does not in the least 

 degree affect the question of the habit and instinct involved in plant- 

 life. The habit is merely manifested through such growth ; behind and 

 above the structural modification and growth are the forces or con- 

 ditions of which that growth is the result. Through similar habits, 

 plants are enabled to overcome the difficulties and disadvantages of 

 their lives, just as the animal may adapt itself to the exigencies of 

 any unwonted condition. Thus, when the field of wheat or corn is 

 laid by the storm, the habits of the plants may aid in recovering their 

 lost position. Resting horizontally on the ground, the under side of 

 the wheat-stalk grows more quickly than the upper side, and in this 

 fashion, adjusting itself to its difficulty, the recumbent stalk is forced 

 upwards to its erect posture. 



More subtle, because the conditions are more difficult of inves- 

 tigation, are the relations between plants and light. That light plays 



