106 The Individual Tracks 



parts of plants, which normally cannot form buds, produce 

 such in accidental variations or in varieties. Flower-bear- 

 ing twigs have been observed on a petal of a Clarkia and 

 of a Begonia, on the stem of the compound leaf of Lyco- 

 persicum, and on the leaves of Levisticum, Siegesbeckia, 

 Rheum, Urtica, and Chelidonium. Caspary saw more 

 than a hundred of them on a petiole of Cucumis. Every- 

 one is doubtless familiar with the flowers on the glumes 

 of the variety of barley cultivated as Hordeum trifurca- 

 tum. 



Some leaves can take root when cut off and stuck into 

 moist ground. I saw those of Aucuba and of Hoya car- 

 nosa keep alive, in this way, for two years, without form- 

 ing buds; some are said to have existed for seven years 

 in this condition. 21 Whether buds are ever developed from 

 the roots of such leaves, either normally or after wound- 

 ing, seems to be unknown. But this is not at all impossi- 

 ble, and in general the whole case deserves to be more 

 thoroughly investigated. Other leaves fail to take root 

 under like conditions, and simply perish. But those of 

 the Crassulaceae, and of bulbous plants, grow buds from 

 their base. Here, too, the line of demarcation between 

 somatic tracks and secondary germ-tracks is evidently not 

 a sharp one, at any rate not qualitative. 



Finally, we have still to emphasize the fact that very 

 frequently the power of reproduction is restricted to 

 youth. This is most clearly shown by the callus-forma- 

 tion of woody plants, where the still living older cells of 

 the bark and the wood usually do not take any part in it. 

 In the petioles of plants that are rich in juice, as Peper- 



21 I have since succeeded in keeping a rooted leaf of Hoya car- 

 nosa alive for more than six years. It did not produce any bud. de V. 

 1909. 



