66 ON THE PROPAGATION 



the law, on the other hand, occur with exceeding frequency, 

 for whole definite parts of leaves can be made to bring 

 forth young plants. If, for example, a leaf of Bryophyllum 

 calycinum is placed upon moist earth, young plants are 

 developed from all the indentations of the leaf, and these 

 can only derive their existence from the extraordinary deve- 

 lopment of certain, appointed cells (PI. in. Fig. 5). The 

 same phenomenon occurs on broken surfaces of detached 

 leaves of the beautiful scarlet-flowered Echeverias, and in 

 many other succulent plants, as also in the Orange-tree. 

 Gardeners take advantage of this phenomenon to multiply 

 these plants, and even in the Middle Ages, an Italian, 

 Mirandola, travelled about, boasting of a secret art by 

 which he could make trees out of leaves. If a notch is 

 made in one of the thick veins of the splendid Gesneria, a 

 new young plant is produced on the broken surface in 

 about a week. 



3. In other plants, we find little protuberances formed 

 regularly and spontaneously upon the leaves, still attached 

 to the stem, and at the points of these, buds which send 

 off rootlets below, thus constituting new plants. This 

 peculiarity is especially common in many Ferns and 

 Aroideae, the allies of the Calla athiopica, or Trumpet-lily, 

 as it is called. The situation where these protuberances 

 and buds are produced, is not indeed perfectly definite 

 here, but it is so far regular that certain parts of 

 the leaf, namely, the angles where veins separate, exclu- 

 sively possess the power of forming them. When such 

 a leaf dies in the natural course of vegetation, these buds, 

 alone retaining vitality, fall to the earth and grow up 

 into perfect plants. Here, therefore, exists an actual 

 natural propagation, or reproduction of the individual ; 

 whereas, before, it depended principally upon external 

 influences. 



