MICHIGAN ACADEMY OF SCIENCE. 



51 



in the complete culture is less than that of leaves of seedlings 

 groM'n in a solution lacking an element. 



2. The assumption that the amount of photosynthate in leaves 

 is an indication of energetic growth is far from true. In a com- 

 plete solution as seen from the result, the leaves contain the least 

 amount of photosyntliate, while the solutions lacking potassium, 

 calcium and pliosphorus respectively, show the greatest gain in 

 weight. This by no means indicates metabolic efiSciency in plants 

 growing in solutions lacking potassium, calcium, and phosphorous, 

 respectively. 



3. These results suggest that the explanation lies in a reduced 

 translocation and a retarded photosynthesis. To test this, three 

 sets of cucumber seedlings were grown in the various solutions. 

 Two sets were used to determine the gain in dry weight per ghm2. 

 Before dawn the leaves from the third set were detached, the cut 

 surfaces of the petiole sealed with melted paraffin and then re- 

 turned to their respective solutions. The results are seen in Table 

 II. 



TABLE II. 



Nutrient solution. . . . 



Complete 



Iron omitted 



Nitrogen omitted. . . . 

 Potas.sium omitted . . 

 Phosphorous omitted 

 Magnesium omitted . 



Gain in dry weight.s. 



Uncut. 



0.16974 gr. 

 0.3.5160 gr. 

 0.29990 gr. 

 0.178.50 gr. 

 0.64680 gr. 

 0.108.50 gr. 



Detached. 



. 6.5294 gr. 

 . 6.5884 gr. 

 0.44760 gr. 

 . 2.59.50 gr. 

 0.89920 gr. 

 0.08920 gr. 



Gain in % 

 of detached 

 over uncut. 



74% 

 4.5% 

 32.9% 

 31.3% 

 28.1% 

 —0.17% 



It shows that the increase of dry weights of detached leaves 

 exceed that of the uncut by a very large margin. It is also seen 

 that the greatest per cent gain was in the complete solution, and 

 that this is the average amount of photosynthate made under 

 greenhouse conditions. This experiment further lends support to 

 the hypothesis that the absence of an element retards translocation 

 of tlie photosynthate. The above data also bear out the theory 

 that tlie rate of ^photosynthesis is impaired when an essential ele- 

 ment is lacking. 



It must be remembered that this study is merely preliminary, 

 but our present data in general indicates that the process of photo- 

 synthesis is greatly modified by absence of a certain element. The 



