yet it must be confessed that this is the very practice employed by- 

 some cucumber growers. In determining the relative carbon assim- 

 ilation taking place in leaves exposed to different qualities and var- 

 ious layers of glass, we made use of leaves that were free from 

 starch. In these experiments we compared a single light of 

 clear glass with double lights of the same quality, also single 

 lights of second quality with double lights of second qual- 

 ity. Most of our experiments were made with second quality 

 glass, and where two lights were employed they were about 

 an inch apart. In other experiments we tested the difference between 

 one light of clean and one of unclean glass, also between one light 

 of clean and two lights of unclean glass, and between clean glass 

 and whitewashed glass. These experiments were always carried out 

 during a bright sunny day and the time of exposure was not over 

 six hours, after which the plants were taken out, their leaves removed, 

 boiled, bleached and treated with iodine. The iodine solution col- 

 ored the starch blue or bluish-black, and, if little or no starch was 

 present, the leaves would attain only a slight blue or no coloration 

 whatsoever. In other words, where the starch reaction was obtained 

 carbon assimilation had taken place. When the plants had been 

 subjected to either one or two lights of glass of inferior transmitting 

 qualities, and the leaves treated as above, the results were practically 

 the same, namely, they showed a little blue coloration of the leaves, 

 or in some cases almost none. This showed, as nrght be anticipated, 

 that carbon assimilation under such conditions was greatly interfered 

 with : on the other hand, good deep coloration predominated in 

 leaves of those plants subjected to one light of clean glass, showing 

 that carbon assimilation was active. Figure 6 shows photographs 

 of two series of cucumber leaves. The darker or bottom leaves m 

 each series are those which were placed behind one layer of clear 

 second quality representative green-house glass ; the upper ones or 

 lighter leaves are those in which the light had to pass through two 

 layers of unclean glass of the same quality as above. It will be 

 seen by a comparison of the lighter and darker leaves in the two 

 series that the difference in carbon assimilation was considerable, 

 and, were cucumbers subject to such conditions throughout their 

 period of life, the differences in the growth of the vines and the pro- 

 duction of fruit would be appreciable. The cork experiment showa 



