662 



"summer leaf fall" in that the lowering of the daily light intensity, follow- 

 ing the beginning of summer, brings about a lowering of the (absolute) 

 amount of light, for the plant concerned, below the minimum, whereby an 

 immediate loosening of the leaves is caused. 



The amount of bloom for each plant depends, of course, upon the 

 abundance of the carbon assimilation, hence shaded speqimens bloom less. 

 Exclusively diffuse light delays the time of blooming and can prevent the 

 complete ripening of the fruit, so that the seed will atrophy'. 



There are cases where plants, with a previously abundant assimilation, 

 are placed in the shade before their blossoms develop. In the dark, the 

 blossoms appear later, as a rule. Their color is paler and at times white; 

 their size and amount of substance less and the peduncles not infrequently 

 longer-. If however, the leaves are left in the light and only the branches, 

 bearing the blossom buds, are darkened, then, according to Kraus^ the 

 flowers, with a few exceptions, develop completely. 



We have considered in the previous section the thin-walled condition of 

 the cell elements in etiolated plants. 



The Lodging of Grain. 



The lodging of the stalks for a long period effects a loss in quantity 

 and quality of the harvest. It is the more dangerous the more the bending 

 of the stalk approaches actual breaking over. Investigators were inclined 

 earlier to assume one single cause for this lodging until later observations 

 determined that very different factors can come into effect and that, accord- 

 ing to the causes, the breaking over of the stalk takes place sometimes at 

 the base in the soil, sometimes close above this point, or higher on the stalk. 



Thus we know now that frost injuries often produce weakening of the 

 stalks which without, or (usually) with the later co-operation of some fun- 

 gus, initiates their falling over. Further, eating by insects, breaking from 

 the wind, hail, long continued rainfall, not infrequently cause a direct falling 

 of the stalks. 



While, however, the majority of the factors named cause a lodging of 

 the grain in spots so that stalks remain standing upright between these 

 places, the actual lodging most feared by the agriculturalist is the one 

 occurring in continuous areas, due to weak development of the bases of 

 the stalks. 



L. Koch"*, who has definitely shown by experiments that this results 

 from a lack of light, produced artificially the phenomena of lodging by 

 shading the stalks. The experiments made earlier by Gronemeyer° were 



1 Passcrini, N., Sopra vegetazione di alcune piante alia luce solare diretta e 

 diffusa, cf. Just's Jahresber. 1902, II, p. 628. 



2 Beulayg-ue, Einfluss der Dunkelheit auf die Entwicklung der Bliiten. Bieder- 

 mann's Centralbl. 1902, p. 102. 



3 Kraus, tjber die Uisachcn der Formverilnderungen etiolierender Pflanzen. 

 Pring-sheim's Jahrb. f. wiss. Bot., Vol. VII, p. 209. 



4 Koch, Ludwig-, Abnormc Andeiungeaa wachsender Pflanzenorgane durch 

 Beschattung. 



5 Gronemeyer in Agronom. Zoil. 1SG7, No. 34. 



