Inheritance of Disease-Resistance in Plants. F.T. Brooks. 71 
EXPLANATION OF PLATE II. 
Fig. 1. Germinating Chlamydospore. x 400. 
Fig. 2. Germinating Chlamydospore, showing two germinal hyphae. x 400. 
Fig. 3. Microphotograph of Chlamydospores germinating in onion juice 
hanging drop. (A) Germinating Chlamydospore shown in detail in 
figs. 4 and 5. 
Fig. 4. Formation of Sporidia (c) after 48 hours in onion juice hanging drop. 
x 400. 
Fig. 5. Appearance of same hypha as in fig. 4 after 13 days showing budding 
of sporidia whilst attached to hypha. x 400. 
Fig. 6. Sporidium budding in onion juice hanging drop. x 400. 
Fig. 7. Germination of Sporidium, one polar germinal hypha. x 400. 
Fig. 8. Germination of Sporidium, two polar germinal hyphae. x 400. 
Fig. 9. Young onion seedling showing sporulation in collar. 
Fig. ro. Hyphae in root-hair of onion grown in smutted soil. 
Fig. rr. Microphotograph of T. S. onion leaf showing distribution of spore 
masses, 
Fig. 12. T. S. onion leaf showing spore masses in intercellular spaces. x 400. 
Fig. 13. L.S. onion leaf showing sporogenous hyphae and developing Chlamy- 
dospores. x 400. 
Fig. 14. Branched haustorium in host cell. x 400. 
Fig. 15. Developing Chlamydospore. x 1000. 
Fig. 16. Developing Chlamydospore. x 2250. 
Fig. 17. Developing Chlamydospore, investing hyphae becoming septate. 
x 2250. 
Fig. 18. Young Chlamydospore showing nucleus and nucleolus. x 2250. 
THE INHERITANCE OF DISEASE- 
RESISTANCE IN PLANTS*. 
By F. T. Brooks, M.A. 
Soon after the re-discovery of Mendel’s law of inheritance in 
Ig01I, certain human diseases under suspicion of being trans- 
mitted hereditarily, were examined, chiefly from the statistical 
standpoint, by tracing the incidence of disease in families of 
known pedigree. In this way it was found that some of these 
maladies, such as colour-blindness and haemophilia, were trans- 
mitted from one generation to another essentially according to 
Mendel’s law, notwithstanding certain complications which can 
now be explained. It is now known that these particular 
diseases are sex-linked, the mother transmitting the defect in 
obvious form to her sons and not to her daughters, in whom 
the disease is usually either absent or latent. 
As regards plants, it has long been clear that some varieties 
* Paper read at a meeting of the Association of Economic Biologists, 
September 1920. 
