\-.\Rii:(;.\ri()N 149 



leaf this bud will produce a \aricj2;atcd brancli and from this 

 the whole plant will be again infected. 



Different species of the Malvacea^ differ widely in their 

 susceptibility to the disease. Thus, Lavdlcni cirhorfu L. is 

 entirely immune, KUaibcVia -cilifoiia Willd. shows much in- 

 di\idual variability, some specimens being immune, while 

 others are susceptible, and other species, such as Jhiitilon 

 sir'uiliiiii Dicks., A. Selloiiuuiiim Reg., A. lud'ictim (L.) 

 Don., etc., are uniformly susceptible. 



Infection can only take place in relatively young tissues 

 and the length of time required for infection is very different 

 in the difierent species and under different conditions, but at 

 least some days are required, thus indicating that the toxin 

 is not carried by the transpiration stream. The same might 

 be inferred frnm the complete failure to secure an aqueous 

 extract which will produce infection. Girdling experiments 

 with Abutiloii Ax-'iccuinic Gaertn. show that the toxin must 

 be carried by the bark as no infection takes place on any 

 part of the plant separated by a girdle from the variegated 

 region of the plant, whether the latter is above or below 

 the girdle. 



The nature of immunity from the disease as manifested 

 by certain species has been in^•estlgated also. It is found 

 that when a cion of the immune Ahiitiloii arhorciiiu is grafted 

 upon A. 'rii()>n psojii, and later a cion of A. Indicinii is set 

 into the A. arhori'inn graft, the A. Iiidiciiiii becomes in- 

 fected. This shows the toxin passes into and through the 

 stems of the immune A . cirborciim and that the latter is simply 

 indifferent to it. However, the toxin which has entered 

 into the immune branch is not capable of producing infec- 

 tion when this branch is severed from the ^•ariegated stock 

 and grafteci into another susceptible stock. Another case 

 of immunity is interesting because it inxohed the origination 

 )f a new immune race in an otherwise susceptible species. 

 :e\eral green branches vvcre found upon a \ariegated speci- 



