353 



But, with the sudden upward pressure of the water, the basal region alone is 

 stimulated, thus causing the development of the cleavage layer. 



In foliage Begonias, rubber plants, camelias and many others, the 

 leaves begin to drop in the autumn and winter. Here, the leaf is in a 

 natural, dormant state. Abundant watering in a warm room causes an up- 

 ward current of water which the leaves cannot utili/e. 



Here are briefly a few of my own observations. A Begonia fuchsioi- 

 des which had been forced through the winter in a warmer room, was 

 brought at the end of March into an unheated, but sunny room. Within a few 

 days it dropped all its leaves except the youngest ones. Libonia florihiinda, 

 which had been kept very cold, was suddenly brought into a greenhouse in 

 December for forcing. The plants dropped all the older leaves, while 

 plants remaining in the cold retained theirs. Some specimens of a double 

 white fuchsia were brought into the house in the autumn in order to get 

 early shoots for cuttings. Other specimens of the same variety were left 

 in the cellar until the beginning of March. At this time the tips of all the 

 plants were set as cuttings in a bench with 25 degrees C. soil heat. After a few 

 days the cuttings, from the plants in the cellar, lost their leaves up to the 

 very tips, while the others had not even lost the leaf at the cut surface. The 

 tips of one branch, taken a few days later from a cellar plant, were placed 

 in sand in the cellar, without any especial care and were found in May to 

 have rooted, while the tips from the cellar plants had gone to pieces in the 

 warm case. 



For house plants it may be recommended as a fundamental principle 

 that the plants should be subjected gradually to other vegetative conditions, 

 and the dormant period, upon which every vegetative plant enters, should 

 not be interrupted by an increase in the supply of heat and moisture. 



The Dropping of the Flowering Organs. 



This process takes place in the same way as that of the leaves\ The 

 composite axes of the inflorescences in Aesculus and Pavia are known to 

 separate into their individual parts, which loosen from one another with 

 smooth cleavage surfaces. In the same way, if many fruits are set, a num- 

 ber of half-grown ones are often abscissed to a joint in the fruit stem. 

 The staminate blossoms of the Cucurbitaceae are abscissed at the cleavage 

 layer formed on the boundary between pedicel and blossom, those of 

 Ricinus communis in a line of separation, produced at a joint lying in the 

 lower part of the peduncle. The hermaphrodite blossoms of Hemerocallis 

 fulva and H. flava, left unfertilized, are abscissed by a cleavage layer ex- 

 tending under the base of the blossom through the upper part of the ped- 

 uncle. The cells of the cleavage surface round up and separate from one 

 another. 



1 V. Mohl, H., ijber den Ablosung-Siprozess saftiger Pflanzenorgane Bot. Zeit. 1860. 

 p. 273. 



