Sense-Life and Sensibility 



examples, the light rays are focussed on the lower or 

 floor-walls of the epidermis, they will produce a differ- 

 ence in the illumination of the protoplasm there, and, 

 on his theory, this difference is the protoplasm-stimulus 

 which results in the leaf taking up a proper light position. 



Each individual cell will move until it is in the right 

 light position. There is a difficulty, however, in dis- 

 tinguishing between light as producing protoplasm 

 movement and light as producing assimilation, but the 

 close resemblance between the primitive eyes of animals 

 and these epidermis cell eyes of plants inclines one to 

 Haberlandt's theory.*^ If one could believe, without 

 misgivings, that the older leaves of Haemanthus do really 

 twist sideways so as to allow of a better light position 

 for the younger ones, then one needs no further proof 

 of reason and morality in the plant world, but some 

 confirmation is acquired of these observations.^ 



Young growing roots, stems, and leaves are very 

 sensitive to the earth's attraction or gravity (that is, they 

 are geotropic). In a general way, stems grow up and 

 roots downwards, whilst many runners and underground 

 stems grow horizontally. One of the most remarkable 

 cases is that of the underground rhizome of Solomon's 

 seal which prefers to grow at a definite depth below 

 the surface of the soil. If it is planted too deep, it 

 will grow in a slanting way upwards till it reaches this 

 favoured depth, and will then grow horizontally. If it 

 is placed too near the surface it turns downwards till it 

 gets to its proper level. 



This remarkable behaviour depends upon two re- 

 actions. The upright foliage and flowering shoot, which 

 is a bud springing from the rhizome, seems to perceive 

 the light stimulus, and as soon as it pierces through 

 the soil, the upward growth of the rhizome stops. 



The rhizome itself is influenced by gravity in such 



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