EFFECTS OX HISTOLOGY 831 



Priestley also records the starch distribution and other histological 

 changes which accompany the formation of the plumular hook of an 

 etiolated stem; he describes an interesting non-plasmolysis of the cortical 

 cells of etiolated plants, though the cells of similar regions will show 

 plasmolysis, if tested about 24 hr. after a short exposure to light. Priest- 

 ley and Woffenden (28) report that in etiolated plants there is only a 

 small production of wound cork in response to superficial wounds. 

 The structure of etiolated monocotyledons is reported upon in a paper 

 by Scott and Priestley (32). 



The effect of visible light and darkness on plants, with limited periods 

 of illumination, seems to offer possibilities as an added tool at the disposal 

 of the plant anatomist who may be interested in a more comprehensive 

 knowledge of the possible induced variations in plant anatomy, for 

 example, such features as the primary endodermis, which is often absent 

 or difficult to observe in the stems of higher plants. 



Schloss- Weill (31) described histological differences resulting from 

 etiolation which were due largely to the elongation of cells rather than 

 to an increase in the number of cells, in the stem of an aquatic plant, 

 Ceratophyllum. Kiister (19) includes a number of references to the 

 effects of intensity of light and to light of various colors. 



EFFECTS OF DIFFERENT REGIONS OF THE VISIBLE SPECTRUM 



The effect of lights of different intensities and qualities on the growth 

 of the fern prothallia of Pteris longifolia are given by Klebs (14). Cor- 

 responding to the degree of light intensity, Klebs obtained elongated cells 

 in the thallus in comparative darkness and in red Ught. Under intense 

 illumination and in blue light the cells were short with many cell divisions 

 and there was a broadening of the thallus. 



Pfeiffer (25) has given us an account of some of the anatomical 

 differences which are recognizable in certain dicotyledons, including 

 the soy bean {Glycine soja), sunflower {Helianthus cucumerifolius) , 

 and four-o'clock {Mirahilis), grown under various colored lights. These 

 plants were grown out-of-doors and in the special greenhouses of the 

 Boyce Thompson Institute for Plant Research which included a "visible- 

 spectrum" house (vs, 7200 to 3900 A), a^ full-spectrum house (/s, 7200 to 

 2900 A), a blue house (6, 5850 to 3350 A), minus violet house {mv, 7200 

 to 4710 A) and a red house (r, 7200 to 5260 A). However, the intensity 

 of the light in these houses varied so that vs and fs were at sUghtly more 

 than half the Ught intensity of the out-of-doors, h had only about one- 

 sixth of the intensity of vs and fs, while r had slightly more than half 

 of the intensity of vs and fs. The summary of this report places the 

 emphasis upon comparisons of the total amount of tissue development of 

 stem, leaf, and root. This study also shows definitely that the quality 

 of the hght affects the thickness of the leaves, for though the light in r 



