78 THE AMERICAN NATURALIST. [Vol.LVI 



plastids or other cytoplasmic elements of a single cell are 

 dissociated. 



The behavior of ^'natural" periclinal chimaeras of 

 Pelargonium, noted by Baur (1909), and of Pelargonium 

 and several other forms, described by Bateson (1919), all 

 of which involve green and white regions of the plants 

 and some of which produce reverse periclinal chimseras, 

 is fundamentally the same as that of graft-hybrids. The 

 manner of origin of these natural chimaeras is unknown, 

 but it is quite possible that they arose as somatic muta- 

 tions. 



The case of Bouvardia also, as reported by Bateson 

 (1916), is presumably of quite the same order as the 

 examples noted above, though its behavior is strikingly 

 different in detail. Varieties of Bouvardia that are 

 maintained true to type by propagation from stem cut- 

 tings produce plants with very different flower form, size, 

 and color when propagated by root cuttings. While this 

 behavior is not to be taken as positive proof that these 

 varieties are natural periclinal chimaeras, it is quite in 

 keeping with such an assumption. Since in normally 

 produced buds of the stem both the epidermis and the 

 deeper lying tissues are maintained through direct cell 

 lineage, while the roots produced by stem cuttings arise 

 from the plerome and break through the periblem and 

 dermatogen, forming these parts anew, sprouts that de- 

 velop from the roots must have the genotype of the stele 

 rather than that of the cortex or epidermis. 



From the results of critical investigations cited in 

 this account, it is evident that vegetative variations are 

 due to diverse causes. Some are certainly due to somatic 

 mutation of genes ; others are as certainly due to chromo- 

 some aberrations; and still others have been somewhat 

 definitely shown to involve a vegetative segregation of 

 plastids or other cytoplasmic elements. There are many 

 problems relating to these several types of behavior that 

 are in great need of further critical study both genetic 

 and cytological. The results of future research will de- 

 pend in large measure on the choice of favorable ma- 

 terial. Quantitative data are of the greatest importance 



