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many plants can endure and still show the familiar characters of 

 so-called etiolated forms. Plants grown in dark chambers to 

 which a meager amount of feeble diffuse light is admitted show, 

 in my experience, more marked "etiolated" characters than 

 when grown in the dark room. While there is a wide difference 

 in the response of plants to varying intensities of light, in a gen- 

 eral way it may be stated that nearly all will endure a surprising 

 amount of illumination without receiving a sufficient stimulation 

 to enable them to accomplish the morphological differentiation 

 that is associated with light. . The potato vine furnishes one of 

 the best examples that I recall of the amount of light that a plant 

 can endure without loss of etiolated characters. This difference 

 in behavior of plants in feeble light and in darkness amounts to 

 a demonstration of the non-paratonic action of light upon many 

 plants at least. When growth occurs in absolute darkness the 

 environment is so unfavorable that pathological conditions soon 

 arise, or the vital processes are carried on under such abnormal 

 conditions that it often appears impossible to interpret the reac- 

 tions or explain them as 'due to any particular cause. The con- 

 siderable variation that is often to be seen in a series of any 

 species of plant is doubtless an illustration of this fact. The 

 entire vital mechanism of the plant is out of order through lack 

 of the normal controlling and directive impulses. Under such 

 circumstances a factor of little moment or unmeasurable in its in- 

 fluence may now become a controlling force in producing a cer- 

 tain development. I have often had occasion to note the marked 

 influence that a slight increase in the humidity has upon growth. 

 Shoots of potatoes produced a more rapid and pronounced elon- 

 gation when covered than was the case with stems growing be- 

 side them, though both were at first in an atmosphere containing 

 50 per cent, of moisture. Without doubt this reaction is largely 

 attributable to the amount of moisture furnished to the reserve 

 food in the tuber. In the same way tubers and bulbs usually 

 develop more vigorous growths when planted than when laid 

 upon moist sand or sphagnum. This is true even when they are 

 covered with cans that ensure a high percentage of moisture to 

 the plant. It is possible that the manner of presentation as well 



