286 



The plants were grown in a greenhouse with a day temperature of about 

 21 degrees C. and a night temperature of about 16 degrees C. However, 

 on bright, sunny days, the temperature went as high as 27-30 degrees 0. 



The plants were arranged upon the bench with enough distance be- 

 tween them to allow them to receive light from all sides. This was neces- 

 sary in order to avoid distortions due to overcrowding. 



In selecting the plants, an attempt was made, as far as possible, to 

 select only tliose which were representatives of large families. Those used 

 were the carnation, chrysanthemum, geranium, bean, corn, and the onion. 

 At the same time they also represent three modes of reproduction; namely, 

 by seeds, by bulbs, and by the ordinary cutting or slip. 



In making a study of the gross difference the following points were 

 noted: The size of the plant, the length of the petiole, size and color of the 

 leaves, diameter of the stems, length of the internodes. and size and 

 abundance of the roots. For the minute differences, the structures of the 

 leaf, stem, and roots were studied. 



In counting the number of stomata sections were taken from various 

 parts of the leaves. The sections were then placed, under the microscope 

 and a spot chosen at random. Twenty counts were made for each side of 

 the leaf and the average taken. 



The bulbs of the onion and the seeds of the corn and bean were planted 

 directly into the five-inch pots in which they were to remain. On the 

 other hand, the rooted cuttings of the carnation, chrysanthemum, and ger- 

 anium were first planted in two and one-half-mch pots and later trans- 

 feiTed to four-inch pots, in which tliey were allowed to remain. 



A close study of the changes in the gross sti-ucture, due to the varia- 

 tions in the soil, show that the effect of a heavy clay upon a plant is 

 almost the same as that of a sand. This may be partly explained by the 

 fact that although a clay soil is very rich in plant foods, the roots find 

 such difficulty in i>enetrating it that the greater part of it is unavailable. 

 Hence, the plant suffers in the same manner as when grown in sand, which 

 is poor in plant foods. 



A change in soil was found to result in: 



First.— A decrease in size from the loam to the sand. In all cases the 

 sand produced a dwarfed growth. 



Second.— A decrease in leaf surface from loam to sand. In no case 

 was the leaf surface in the sand over one-half that of the loam. 



