287 



Third.— A variation in color. The clay soil gave a very dark green leaf, 

 while that in the sand was always of a sickly, yellowish green. 



Fonrth.— A decrease in length of petioles from loam to sand. 



Fifth.— A decrease in the diameter of the stem from loam to sand. 



Sixth.— A decrease in the length of the internodes from loam to sand. 



Seventh. — A decrease in the mass of roots from the loam to the sand 

 with the exception in the case of the onion. However, when the size of 

 the plant is taken into consideration, the mass of roots of the plants in 

 sand was always relatively the greatest. 



As a resnlt of these nnmerons variations, the plants in the sand have 

 a stnnted groAvth above soil and an increased growth in the soil. This 

 is also trne of the clnj, bnt not to snch a great extent as in the sand. 



The changes in the histological structure are not so general. Those 

 which do take place are more for specific rather than general cases. The 

 changes which are general may be summed up as follows: 



First. — A decrease in the transpiring surface from the loam to the 

 sand. 



Second.— A decrease in the relative size of the woody tissues of the root 

 from the loam to the sand. This decrease was due to a variation in the 

 number of cells rather than to tlieir size. 



Third.— A larger number of crystals for the clay soil than either of the 

 other two. This was true in the two plants in which the crystals were 

 found, the carnation and the geranium. These crystals were found both 

 in the stems and the leaves. 



Fourth.— A greater wood development in the loam than in either of the 

 others. This increase was not due so much to an increase in the size of 

 the cells as to their niimber. 



There Avas (luite a variation in the number of stomata, but these varia- 

 tions were specific and not general. In some cases the loam had the 

 highest average, in others the clay, bnt in most cases the greatest number 

 were in the sand. In one case, tlie corn, the loam showed the greatest 

 average for both sides of the leaf. In the bean, the clay gave the greatest 

 average, while in the onion, carnation and geranium the sand gave the 

 most. (See table.) 



In five cases oiat of the six. the loam gave the thickest leaves. In the 

 sixth case, that of the carnation, the clay gave the gi'eatest average. 

 This increase in thickness was caused by a general increase in thickness 

 of all The tissues of the leaf. 



