FUNGUS RESISTING PLANTS. 379 
In the different “constitutions” thus shown by the various varieties 
or strains we have, clearly indicated, a basis for the plant-breeder to work 
on in breeding disease-resistant plants. The existence of different “con- 
stitutional”’ characters in the strains of plants they have bred has of 
course long been known to practical horticulturists. But I should like 
here to point out the fact that varieties and “races’”’ of plants have each 
a definite ‘‘constitution’’ with respect to fungus disease, and that this 
fact is now capable of scientific demonstration. 
TABLE. 
Sown on 
Oidium on =~ S S s & | s = | S 3 
, oy" 4 48 10 42 9 a edt 11 ) 1é 20 
B. interruptus | +(") + (*)/ — (| — 09 #709 ery) — 9) 4099 = 
B. hordeaceus + (72) | +) IP = (") aR: (’) | aie 2(”) } —('5), — (8) + (2) | — (73) 
P| = 0) 09) 0) 
’ | 22) | 6 6 
B. commutatus —('3) | —(°) BS Ce) Lae ) oF (°) — (#8) | — (1) es ) —(7) 
Ble eee Gs) ede) 
B. racemosus — (!*) | + (?”) —(°) 
B. velutinus —(*) t= ((8) + ('%) | —() , —@ ) +(?) 
B. arvensis —(*) ines (@) 
B. tectorum | + (8) af 
B. arduennensis — —(°) — (3) | | ss — (*) 
+ =full infection +2 = ‘ subinfection ’ — =no infection 
The number of leaves of each species inoculated is shown within parenthesis. 
As illustrating the manner in which a plant’s “constitution ”’ shows 
itself with respect to a fungus disease, I may refer here to some experi- 
ments which I carried out recently at Cambridge and at Kew. The 
fungus used was the Corn and Grass Mildew (Hrysiphe Graminis DC.). 
As a result of over 2,000 inoculation experiments which were made, 
I was able to show that by using the index of the reaction to the attacks 
of “ biologic forms”’ of the fungus,* the presence of definite physiological 
(or constitutional) characters in a plant can be demonstrated. We find, 
first, that distinctive ‘constitutional’’ characters in this sense exist 
* A detailed account of these experiments, and the results obtained, will be found 
in the following papers: Beihefte z. Botan. Centralbl. xiy. 261 (1903); Annales 
Mycolog. ii. 255, 307 (1904); Uc. iii, 172 (1905); The New Phytologist, iii. 55 
1904) ; lc. iii. 109 (1904). | 
