1 qo THE PLANT WORLD 



men of AbiitUon str'uitum Dicks, (i. e. A. Thompsoni hort.). 

 These were grafted into normal stocks of A. struitiim, and 

 the plants so produced proved to be immune, though all 

 ordinary A. str'uitiiiu plants are susceptible. 



In case of the immune Lavateni arborca L. there is no 

 transmission of the toxin through the immune tissues and 

 any susceptible cion set directly into Lavatera wood remains 

 green regarclless of the contact of this Lavatera-stock with 

 diseased tissues at some other point. 



In the first of the cited papers Baur suggests that the 

 "mosaic disease" of tobacco is of the same nature as the 

 infectious chlorosis of the Malvaceae. There is this differ- 

 ence, however, that the tobaccos may be infected by means 

 of extracts, while the toxin of the \'ariegated mallows seems 

 to be incapable of existing outside of the Tu'ing cells. This 

 is not considered a difference in kind between these two 

 toxins, however, but only in degree. 



Variegation of precisly similar nature to that of the 

 JVialvaceae is demonstrated in Li^iistntni z-iilg^are, LabiiDi- 

 iiin viilgcire, Fraxiuus pitbcscois, Sorbiis Ancuparui and 

 Ptelea trifoliatu, and doubtless many other species will be 

 found to he subject to some form of infectious chlorosis. 



Not so much has been done yet in the in\estigation of the 

 inheritable type of variegation, but it seems that many cases 

 in which variegation forms a rather definite pattern, as for 

 instance when it affects only the margins of the leaves, this 

 character is hereditary. 



The variegation of A iitinliiiiiim majiis is the only case 

 fully studied. This presents one of the interesting cases 

 of Mendelian inheritance on record. 1 he green specimens 

 are homozygous and breed true when interbred, producing 

 no variegated offspring. When two \ariegated plants are 

 crossed together the offspring present the unexpected ratio, 



2 variegated: i green. To explain this ratio, 2:1, the as- 



