172 PLANT GROWTH SUBSTANCES 



cambium was just as active. There was a greater lignification of the 

 vascular elements and the fibers, and the cells were much larger than in 

 plants grown without calcium (Fig. 22). Except for the size of the 

 vascular bundles, the structure of the control plants and of plants grown 

 without calcium but treated with a-naphthaleneacetamide was very 

 similar. 



During the winter of 1948 the experiment was repeated under long- 

 day photoperiod and at a temperature of 65° F. Twenty days after the 

 start of the experiment deficiency symptoms were apparent in plants 

 grown without calcium. Twenty-four days after treatment deficiency 

 symptoms were also becoming apparent on plants grown without calcium 

 but treated with a-naphthaleneacetamide. After forty-four days plants 

 grown without calcium, and those grown without calcium but sprayed 

 with a-naphthaleneacetamide showed severe calcium deficiency symp- 

 toms. The plants were sampled for anatomical observations at this time. 

 The fourth internode showed structural abnormalities typical of calcium 

 deprivation in plants grown without calcium and plants grown without 

 calcium but treated with a-naphthaleneacetamide (Fig. 24, 25, 26, 27). 

 The experiment was repeated and similar results were ob'^ained. 



The question then arose as to why results similar to those obtained 

 the previous late spring at 70° F. were not secured. Could the difference 

 in temperature account for the difference in the effect of a-naphthalene- 

 acetamide on delaying calcium deficiency symptoms? 



The experiment was again repeated in the greenhouse, except that 

 it was carried out at a temperature of 75° F. After twelve days plants 

 grown without calcium showed symptoms which rapidly became more 

 severe. After sixty days the plants grown without calcium were dead 

 and those grown without calcium but treated with a-naphthalene- 

 acetamide showed no calcium deficiency symptoms. After seventy-five 

 days only slight symptoms of calcium deficiency were apparent in plants 

 grown without calcium but treated with a-naphthaleneacetamide. At 

 this time all plants were sampled for anatomical observations. 



The anatomical structure of the fourth internodes of these plants 

 corresponded closely to those of the first experiment at the warmer 

 temperature. The stems of plants grown without calcium had small 

 bundles and small cells, resulting in a decreased amount of lignification. 

 Plants grown without calcium but treated with a-naphthaleneacetamide 

 showed a structure more closely resembling the normal plant. 



