no 



THE FACTORS 



[Part I 



however forms, as soon as it comes into contact with the nucleus, a vesicle that is 

 egg-shaped or pear-shaped and becomes filled with cytoplasm and nuclei (Fig. 60). 

 After a time the contents of the vesicle become disorganized and transformed into 

 a yellow, granular mass. The nucleus in the meantime has changed its position in 

 the cell, but the terminal point of the mycelial thread follows it, and, in contact with 

 it, repeatedly forms fresh vesicles. In the outer region of the cortex the hyphae live 

 longer and exhibit less connexion with the nucleus or (in the sheath) none at all. 

 Groom attributes, without doubt correctly, the growth of the terminal point of the 



Fig. 58. Fagus sylvatica. Mycorhiza with 

 fungal hyphae. Magnified 9. After Ka- 

 mienski. 



Fig. 59. Thismia Aseroe. Cortex of the myco- 

 rhiza. After P. Groom. 



hyphae in the direction of the nucleus, to chemotropism. The same thing occurs 

 in the case of undoubtedly parasitic fungi, for instance in Puccinia asarina and 

 Hemileia vastatrix, the fungus of the coffee disease, and is quite general in endo- 

 trophic mycorhiza. It is clearly due to a product near the nucleus arising chiefly in the 

 inner cortical layers. The swelling is due to vigorous nutrition, for a similar pheno- 

 menon also occurs in cultures of fungi in nutritive solutions, if the concentration 

 of the latter be increased. That the solution of the starch is to be associated with the 

 formation of proteids in the vesicles is obvious from what has been said before. 



