No. 636] 



GENETIC SK(,l;i:i..\Tl(>\ 



17 



interpretation that they are pcricHiidJ cliiiiiaTas is ])r()b- 

 ably correct for the most part. The fr'mucd l'rhir(i()uh()i> 

 is obviously of this nature. Nevertheless, tlie lad tliat 

 a root-cutting consistently produces a certain type of 

 plant which is not the original does not prove that the 

 distribution, is periclinal. Another possibility is well 

 illustrated by the case of a variegated Spiraea ulmifolia, 

 having the stem, petioles, and (basal) centers of the 

 leaves without chlorophyll.^^ The growing point has 

 the power of laying down green tissue in the lateral 

 areas only, the internodal regions being albinotic. Root- 

 cuttings from this form give albino plants which die 

 after the development of two or three small leaves. Now 

 in this case we can see the distribution of the green and 

 white, respectively, and we recognize that the roots give 

 albino plants because they belong wholly to the albinotic 

 area. On similar lines it is possible to interpret the 

 Bouvardia and other cases. The distribution of the two 

 types in the same plant may be such that one is limited 

 to the root and internodes, while the other is in the nodal 

 structures. 



That considerations of this kind are not fantastical is 

 proved by the genet ical phenomena seen in the case of 

 ''rogues" in culinary peas, which Miss Pellew and I 

 have been investigating for a number of years. The 

 rogue is a peculiar, wild-looking plant, differing in 

 various ways from the type, chiefly in having pointed 

 leaflets. Crosses between it and the type give plants 

 which in their lower parts are intermediate, though turn- 

 ing into rogues as the\ develop. 'l^Iie -elf- fertilized off- 

 spring of rogues and al-o .>t tlie>e 1-', i>lant> are always 

 rogues, and evident Iv ilic t \ i>e (-har;icter> introduced 



