354 



In the same way a fully developed cleavage layer is found in the sepals 

 of Papavcr somniferum, Liriodendron iulipifera, at the time they fall; in 

 the falling parts of the calyx of Mirabilis Jalapa, Datura Stramonium; in 

 ihe petals of Rosa canina, Papaver; in the single corolla of Lonicera Capri- 

 folium, Rhododendron ponticum, Datura Stramonium; in the stamens of 

 Liliiim hulbiferum and L. Martagon, Dictamnus Fraxinella, Liriodendron ; 

 in the stigma of Lonicera Caprifolium, Mirabilis Jalapa and Liliiim 

 Martagon. 



In the majority of cases, the cells of the abscission layer contain no 

 starch, or at least no more than does the surrounding tissue, while, in the 

 leaves and thick sepals and petals of Liriodendron abundant starch is pres- 

 ent. This lack of reser\e nutriment is explained by the rapid formation of 

 the cleavage layer in the blossoms, for which the momentarily transportable 

 nutritive substance is sufficient. In the sepals of Papaver somniferum the 

 cleavage layer is produced in a single night, in the petals of single roses, 

 in the hours of an afternoon. While cell increase seems to occur in the 

 cleavage layer of leaves, it can hardly take place in the petals. The pro- 

 cesses there visible consist only of a more abundant protoplasm, an in- 

 creased porosity and mutual separation, due to a rounding up of the cells, 

 and, at times, a pouch-like enlargement of the cells, whereby the cleavage 

 layer looks velvety. The appearance of the cleavage layer is delayed as the 

 organs are better nourished. 



The Shelling of the Grape Blossom. 



By the term "shelling" or "falling" the winegrower means the dropping 

 of blossoms soon after blooming. In some regions the phenomenon returns 

 annually while, in other localities, it appears only in isolated years, as, for 

 example, in those when wet, cold weather destroys the blossoms. Accord- 

 ing to Miiller-Thurgau's^ investigations, with a low temperature at the 

 time of blossoming, the cells of the stigmas were beginning to turn brown 

 even before the blossom sheaths fell, which indicated death or at least 

 an extensive retarding of the process of pollination. Actually, on such 

 stigmas the pollen grains did not develop pollen tubes at all, or only 

 poorly. The dropping of the petal cap took place ver)' slowly or was en- 

 tirely suppressed. The ovule cases of such blossoms remained for some 

 time, often actually for a long time, but they scarcely enlarged at all. How- 

 ever, since, according to Miiller's discoveries, ringing of the vines is usually 

 beneficial, the low temperature cannot be the direct cause of the incompleted 

 act of pollination and the failure to mature the seed. The dull, cool weather 

 during blossoming is especially favorable for the growth of leafy shoots, 

 which, on this account, require the material stored up for the development 

 of the inflorescence, so that the nutrition is not sufficient for the blossoms. 

 Such a starving of the blossom cluster and, consequently, a more or less 



1 Miiller-Thurgau, t)ber das Abfallen der Rebenbliiten und die Ent.stehuns 

 kernloser Traubenbeeren. Der Weinbau, 1883, No. 22, 



