297 



In this premature breaking forth of the young branches Hes the cause of the 

 "fall of the blossoms." The error in treatment is that the plants are kept 

 too warm and moist and insufficiently lighted for the given stage of their 

 development. While the flower, to be sure, needs warmth and atmospheric 

 humidity for its development, too great moisture in the soil injures it. This 

 incites the leaf buds near the blossoms to a premature exfoliation and these 

 attract the current of nutritive substances to themselves, squeezing out the 

 functionally weak blossom buds. 



In forcing bulbs, especially tulips, we also find such conditions of star- 

 vation of a flower bud resulting from too vigorous a development of the 

 vegetative organs. In the newer cultivated varieties we often find that the 

 flower stalk is not leafless, but has one or two leaves borne on clearly 

 marked nodes. In such examples, the bud is so weak that, when forced in 

 winter, it cannot develop at all, but dries up, because of preponderating leaf 

 growth, resulting from the excess of moisture and warmth. 



An experiment made with V eltheimia glauca may be cited as an ex- 

 ample of the drying up of the flower buds, due to a lack of nitrogen. A 

 vigorous double bulb had been divided several years previously and each 

 daughter bulb had bloomed regularly every winter after this division. When 

 later one of the bulbs was not transplanted, while the other was set in new, 

 rich earth, the inflorescence developed earlier in the former, to be sure, and 

 was more slender, but the flowers dried up before being completely formed. 

 This plant was now given homshavings as a source of nitrogen, without 

 changing the soil in the pot. In the following year the inflorescence appear- 

 ed to be more vigorous and the flowers more numerous; part of them de- 

 veloped and became colored, but not so deeply as those from the bulb which 

 had been transplanted each year. 



It is well known that a supply of nitrogen will increase the product of 

 agricultural plants. 



The Formation of Thorns. 



The formation of thorns, i. e., the replacing of a bud on the end of a 

 shoot by a woody, pricking tip, may be perceived as an indication of the lack 

 of nitrogen. A comparison of figures 37 and 38 (cross-sections of Rhamnus 

 cathartica) shows what changes have taken place. The tissues, indicated in 

 both figures by the same letters, should be compared. We see that in the 

 formation of thorns, the thick-walled elements gain the upper hand, and that 

 even the parenchyma cells of the bark and of the pith have unusually thick 

 walls. A young branch ending in a thorn, can at times form lateral buds at 

 its base, if enough nitrogen is still present for the formation of the meriste- 

 matic centers. But these lateral axes begin to assume thorn-like character- 

 istics early in their development. Ducts may be found as far along on the 

 thorns as leaf buds can be recognized and even for a distance beyond them. 

 These usually disappear in the apical region. 



The elimination of thorns is especially desirable horticulturally because, 

 for example, the thorns of such plants as Crataegus, Pirus communis, 



