April, 1915.] The Inheritance of Size in Tomatoes. 481 



Moisture. The noticeable lack of moisture will cause a 

 plant to become ill -nourished and dwarfed. The moisture con- 

 ditions in the greenhouse were controlled as perfectly as possible 

 and the tomato plants were watered quite often, but even then 

 optimum moisture conditions did not prevail. The lack of a 

 constant abundance of water probably exerted a great limiting 

 influence upon the size of plant. The transpiration of water is 

 directly proportional to the amount of leaf surface and, after the 

 plant has reached a certain mature size, the leaf surface becomes 

 limited as the amount of moisture in the pots is limited. The 

 plants grown in the garden attained a greater size than the potted 

 plants and one of the j^rincipal reasons for this difference was the 

 more constant and abundant supply of soil-water present in the 

 garden environment. There was no corresponding influence 

 upon the size of fruit, as there was no noticeable difference of 

 fruit-size as a result of the different moisture conditions under 

 which the plants were grown. 



Soil. The quantity and quality of the essential nutritive 

 substances in the soil, as well as the physical condition, influences 

 the size of a plant and fruit. Wanning says (b), "Defective 

 nutriment (that is an inadequate supply of one or more substances) 

 may be the cause of dwarf -growth (nanism) ; this has been demon- 

 strated by many physiological investigations." All of the 

 potted plants in these experiments were supplied with a soil as 

 perfectly adapted as possible, both physically and chemically, to 

 the growth of the tomato. And yet, the amount of available 

 plant nutriment in a five-inch pot is necessarily somewhat limited 

 while the available nutriment substances are more abundant in 

 the garden, so that this lack of nutriment in the pots together 

 with the lack of perfect moisture apparently caused the difference 

 in size between the greenhouse and garden-grown plants. There 

 was not enough difference, however, between the soil and moisture 

 conditions of the greenhouse and the garden to cause any appre- 

 ciable change of fruit-size. 



Two experiments were tried to deteniiine the effect of different 

 kinds of soil conditions upon the size of plant and fruit. 



The first experiment was pcrfomied in order to show the effect 

 of the garden conditions upon the size of plant as compared with 

 the effect of the greenhouse environment upon the size of the 

 same plant. In the garden the soil contained more available 

 nutriment and moisture than were present in the pots. A number 

 of plants of the F-1 generation (17-12-2) were grown in the green- 

 house where they attained at full maturity a height of about 2.5 

 feet and a diameter of 1 .."3 feet. One of these plants was afterwards 

 removed to the garden where it grew to be 3 feet high and covered 



(b) See (40) page 5G. 



