EFFECTS ON HISTOLOGY 833 



Kiiop uutricMit sohition. He also constructed some special glass color- 

 filters, which are described. 



Teodoresco found, as he did in a very similar investigation reported 

 30 years previously, that the red end of the spectrum has the same effect 

 as darkness, in reducing the thickness of the leaves and their surface 

 area and in increasing the lengths of the internodes and petioles by an 

 increase in the length of their cells. The effect of the blue-violet light 

 is very similar to the effect of white light, though he found shght devia- 

 tions from this generalization in the responses of Helianthus annuus and 

 Menispermum cocculus. These same general conditions were found in 

 the germination of fern spores. The spores of Pteridium, which can 

 germinate in darkness, gave almost the same response in the red light. 

 However, when the reserves stored in the spore are exhausted, relatively 

 strong photosynthetic action is possible in the red light employed and 

 the elongation may therefore far surpass that obtained in complete 

 darkness. In the sporelings of certain liverworts the red light also causes 

 excessive elongation; often there are long single filaments or germ tubes 

 composed of excessively long cells which have undergone very few cell 

 divisions. The sporelings of Conocephalum and Pellia, two liverworts, 

 when grown in red light are shorter than those grown in white light and 

 longer than those grown in blue light. In these experiments as in many 

 others the shortcomings of the screens employed in respect to giving a 

 restricted spectral region must be taken into consideration. 



Teodoresco (38) emphasizes the fact brought out in his earlier investi- 

 gation (37) that the blue-violet rays appear to be more favorable and" 

 more adequate for the normal form development of the plant than the 

 red rays. 



This investigation, employing plants with reserve foods, supports 

 the view that photosynthesis may take place in the red light, which may 

 in turn support a considerable amount of growth (elongation) which 

 is not brought about by the direct photomorphic effect of this portion 

 of the spectrum. Plants with abundant reserve foods may therefore be 

 expected to respond somewhat better to the blue-violet portion of the 

 spectrum. 



We find a very interesting record by Forster (10) working with 

 another liverwort, Marchantia polymorpha, who used Hiibl's filters 

 (Nos. 2, 11, and 20) and grew the thalli from gemmae under red, green, 

 and blue filters. He adjusted the different filters and his mixed-light 

 controls to the same intensity and found that in general the growth 

 responses under the red filters were as good as under white light; the 

 green light was only about l^o a-s effective as the mixed light of the same 

 intensity and blue light markedly inferior to the red. The air chambers 

 found in the upper layers of the thallus were normally developed in 

 red light; they were formed, but without the special assimilatory cells 



