MOVEMENTS OF GROWTH. 407 



plants. The boxes were blackened inside. Plates of glass could 

 be slipped in to form the front. One box may be provided with a 

 sheet of ordinary glass, another with a single sheet of opal glass, a 

 third with two sheets, and a fourth with four sheets of opal glass. 

 Plants are also, for comparison, grown in complete darkness. We 

 place the boxes in front of the window in a room with a north 

 aspect. Using beans, we shall soon observe that the plants which 

 receive most light produce the shortest stems and the largest 

 leaves. With diminishing intensity of light, due to interposition 

 of the sheets of opal glass, the length of the stems increases, while 

 the size of the leaves diminishes. 



Various plants are able to develop in constant darkness not only 

 numerous leaves and long stems, but also flowers. Thus if 

 Hyacinth bulbs are germinated in the so-called Hyacinth glasses in 

 continued and complete absence of light, they will actually flower. 

 I satisfied myself that the flowers, as regards form and colour, 

 develop quite normally in absolute darkness, behaving therefore in 

 a manner different from most stems and foliage leaves. 3 



It is further of interest to make the following experiment. We 

 raise plants of Phaseolus multiflorus in flower-pots under ordinary 

 conditions. When the primordial leaves have developed normally, 

 and the internodes following the epicotyl are rapidly elongating, 

 we expose the apex of a plant to darkness, leaving the rest of it 

 in bright daylight. This is effected as follows. A stand carries 

 a large metal ring, on which rests horizontally a sheet of thick 

 cardboard with a hole in the middle of it. The apex of the plant 

 is passed through this hole, and tightly fixed in it with cotton 

 wool. Finally we place over the bud a tall cardboard cylinder 

 covered with black paper, with its edge resting on the sheet of 

 cardboard. In the course of two or three days we shall find that 

 the new internodes produced thus in darkness are abnormally long, 

 while the leaves remain small.* 



If this experiment is to succeed well, the plants must be put in 

 a place where, at any rate for a good part of the day, they receive 



* ThU result is not in complete accordance with certain statements of 

 Sachs, Lectures on Plant Physiology, p. 532. In the experiments of Sachs, 

 however, the conditions were not the same as in mine, since his research 

 plants possessed numerous leaves, exposed to the light and vigorously assimi- 

 lating. The darkened leaves attained a considerable size, and the like may 

 also under similar conditions take place in Phaseolus. The whole question, 

 however, demands further experimental examination. Consult Frank, Lehrbuch 

 der Botanik, Bd. 1, and Amelnng, Flora, 1894. 



