4o6 



the soil and the acid secretions of the roots. Injury from superphosphates 

 is, therefore, to be feared even with heavy appUcations only on soils which 

 are poor in calcium, iron and aluminum carbonates. There are only a small 

 number of experiments on this subject. The careful investigations, made 

 at the experimental station in Bernburg, on sugar beets^ fertilized with the 

 monobasic calcium phosphate, i. e., excess of phosphoric acid soluble in 

 water, have shown that the sugar content does not decrease and also that 

 the amounts of beet substance and non-sugar have remained the same as in 

 normally fertilized beets. 



So far as my own experience goes, an excess of phosphoric acid may 

 manifest itself in a shortening of the root system, — the usual result of 

 culture in all highly concentrated solutions, and also in shortening the 

 vegetative period with a premature ripening of the crop. The plants do not 

 develop fully, the leaves turn yellow prematurely, and, accordingly, the 

 yield is smaller than it would otherwise have been. 



g- 



Excess of Carbo>si Dioxid. 



Experiments on the effect of carbon dioxid content in the air and soil, 

 greatly in excess of the normal, have led to contradictory results. While 

 some observers have recognized only injurious eft'ects, others report a 

 satisfactory development. These apparent contradictions may be due to 

 the fact that with carbon dioxid, as with all other nutritive substances, the 

 effect depends upon how simultaneous the activity of all the other growth 

 factors may be. The activity of the plants is generally adjusted to the 

 small normal carbon dioxid content of the air'-. They sometimes respond 

 to a greater increase of carbon dioxid by arresting growth, sometimes by 

 increasing it, depending upon whether the carbon dioxid increase occurs 

 suddenly, or gradually, and whether the amount of light and warmth, water 

 and nutrients permits the individual utilization of the increased amount of 

 carbon dioxid. Godlewski" has substantiated this point of view by 

 experiment. 



Our hot bed plants furnish abundant proof of the favorable aff'ect. 

 According to E. Demoussy's investigations*, this is due not only to an in- 

 creased warmth, but actually also to an increase of the carbon dioxid in the 

 air of hot beds, sometimes amounting to more than two thousandths parts. 

 In comparative cultures, the air of the hot bed, which after careful testing 

 showed no ammonia, had furnished nearly three times the harvested weight 

 of plants grown in ordinary air under otherwise similar conditions. 



1 See lecture by H. Roenier; cit. Ulatter f. Zuckerriibenbau 1905, p. 229. 



a Brown, F., and Escombe, F., Der Einfluss wechselnden Kohlensauregehaltes 

 der Liuft auf den photosynthetischen Prozess der Blatter und auf den Wachstums- 

 modus der Pflanzen. — Farmer, J., & Chandler, S., tJber den Einfluss eines tJber- 

 schusses von Kohlensaure in der Luft auf die Foiin und den inneren Bau der 

 Pflanzen. Proceed. R. Soc. LXX. cit. Centralbl. f. Agrik.-Chemie 1903, p. 586. 



y s. Sachs, Arbeit, d. Bot. Instituts zu Wurzburg. Part III. 



■t Compt. rend, de I'Acad. d. sciences 1904. cit. Centralbl. f. Agrik.-Chemie 

 1904, I'art 11, p, 745. 



