1923] Mau: Morphological Characters in Crepis Capillaris 231 



radiation, and (3) duration of exposure. They conclude that the 

 relative length of day is a factor of prime importance in the growth 

 and development of plants, particularly with respect to sexual repro- 

 duction, and in 1922 they confirmed and amplified their work. I 

 have been able to confirm this work to a certain extent. A culture 

 of plants growing in the greenhouse was close to an electric lamp 

 used to maintain a constant temperature in a chamber close by, and 

 the plants that were closest to this lamp flowered first, the arc of 

 flowering spreading out centrifugally. After some time all the plants 

 that were near the lamp had flowered, although the rest of the cultures 

 took nearly two months longer to produce flowers. Moreover, the 

 plants that bloomed first were in a comparatively disadvantageous 

 position during the day, so that the effect of the artificial illumination 

 on the flowering of the plants is all the more striking. This observa- 

 tion was repeated in an attempt to hasten the process of flower forma- 

 tion. Two strains of plants, 0215 and 0217, which were both F^ 

 progeny of crosses made by me, were growing very slowly and were 

 still in the rosette stage by the end of March of this year due to the 

 cold winter. In order to hasten their growth and obtain seed for 

 growing an Fo population, a few of them were placed three feet below 

 a 300 Watt electric lamp surrounded by a reflector every day from 

 6 p.m. to 8 a.m. the next day. Some of them shot out flower buds in 

 about three wrecks from the time the experiment was started. The 

 rest of the plants in the same families which were not subjected to 

 artificial light had in many cases not started to send up the central 

 floriferous axils. The heat from the lamp may also have had a slight 

 effect. 



Moisture. — The plants as they grow in pots in the greenhouse are 

 not subject to much variation in soil moisture because they are 

 watered regularly and the minimum soil moisture necessary for proper 

 growth is usually maintained. The case of the plants grown in the 

 field, however, was different because irrigation water was applied 

 periodically, and owing to the variation in temperature of the days 

 intervening between two successive irrigations, the soil moisture was 

 neither constant, nor was it always above the minimum water require- 

 ments of the plants. Consequently, the flowers gradually got smaller 

 as time elapsed after irrigation until, during the hottest part of 

 the day, the plants would show signs of withering. Measurements 

 were taken at this period and showed comparatively the smallest size 

 in the diameter of the capitula. This difference went up usually 



