46 



THE DAILY MARCH OF STOMATAL MOVEMENT. 



no night opening correlated with mid-day closure, and as rarely 

 showing maximum opening of all the stomata. 



The alfalfa type of stomatal movement is characteristic of most 

 thin-leaved mesophytes. The normal light -curve of alfalfa (fig. 6) 

 shows stomatal movement under the most favorable conditions, and 

 is the same kind of curve as that produced by a cereal under such 

 conditions. Then, as these become progressively less favorable, 

 mid-day closure appears, increasing to complete closure, which in 

 turn becomes more and more prolonged until the stomata are closed 

 all day. With the appearance of mid-day closure, night opening also 

 develops and increases with increase of day closure. The final result 

 is a partial opening of stomata all night and complete closure all day. 



The plants studied with this type of movement are: 



Melilotus alba, sweet clover. 

 Trifolium pralense, red clover. 

 T. repens, white clover. 

 Pisum sativum, garden pea. 

 Lathyrus odoratus, sweet pea. 

 Phaseolus nanus, navy bean. 

 P. lunatus, lima bean. 

 Beta vulgaris, sugar-beet. 

 B. vulgaris, blood-beet. 

 Chenopodium album, lamb's-quarters. 

 Rumex patientia, western dock. 

 R. crispus, curly dock. 

 Brassica napus, rape. 

 B. campestris, turnip. 

 Raphanus sativus, radish. 

 Brassica campestris, rutabaga. 

 Papaver somniferum, poppy. 

 TropCBolum major, nasturtium. 



Amaranthus retroflexus, pigweed. 

 A. grcedzans, little pigweed. 

 A. blitoides, carpet- weed. 

 Polygonum aviculare, knotweed. 

 Malva rotundifolia, cheeses. 

 Pastinaca saliva, parsnip. 

 Daucus carota, carrot. 

 Lycopersicum esculentum, tomato. 

 Citrullus vulgaris, watermelon. 

 Cucumis melo, muskmelon. 

 C. sativus, cucumber. 

 Helianthus annuus, sunflower. 

 Arctium lappa, burdock. 

 Lactuca scariola, prickly lettuce. 

 L. saliva, lettuce. 

 Taraxacum officinale, dandelion. 

 Ribes aureum, golden currant. 

 R. ritbrum, common currant. 



The trees whose stomatal movement was investigated were apple 

 (Mains sylvestris) , pear (Pirus communis), Elberta peach (Prunus 

 persica), sweet cherry (Prunus cerasus), and Lombardy poplar 

 (Populus nigra italica). These, as well as California privet (Ligus- 

 trum japonicum) , must be classified with the alfalfa group, since night 

 opening does not occur under favorable conditions. On the other 

 hand, no mid-day closure was found in any of the series, as they 

 seemed to be little affected by evaporation. It is impossible to state 

 the water-content about their roots, but there is good reason to 

 believe that the soil was moist at all times. The behavior of their 

 stomata resembled the normal light-induced movement in alfalfa at 

 the times when the stomata of alfalfa showed considerable day closure. 

 This was probably due in large measure to the great balance of water 

 on hand in the trunk and branches of the tree, and to the high 

 water-content within reach of the roots. 



The third group contains the larger number of fleshy-leaved 

 plants as well as some thin-leaved ones. Under conditions of high 



