92 PHYSIOLOGY OF NUTRITION. 



particularly the ectotropic form of it, since the hyphas of the 

 fungus do not penetrate into the cells of the root, at most in- 

 sinuating themselves between the epidermal cells. The Mycorhiza 

 is made up of the root fibres, and the fungal hyphse living in 

 symbiosis with the root. The latter (root hairs being of course 

 absent) absorb the water and mineral substances of which the 

 beech (or other plants provided with Mycorhiza) has need. Pro- 

 bably also nitrogenous organic substances are taken up from the 

 soil by the Mycorhiza. 



"We collect some humous soil from a beech wood. The material 

 is well broken up, mixed, and sieved. We fill a few flower-pots, 

 about 20 cm. in height, and the same in diameter, with this soil, 

 and moderately moisten it. Some of the pots are at once 

 employed for the following experiments (after Frank), the 

 others being first sterilised by exposure for some hours to a 

 temperature of 100 C. in a drying chamber. The pots are 

 covered while in the drying chamber by pieces of glass. We now 

 place in the soil of each pot a few beech seedlings. These are 

 best obtained by germinating beech-nuts, just after gathering in 

 autumn, between folds of moist blotting-paper. The seedlings 

 are transferred to the pots after twelve to eighteen days, and these 

 are then put in the cool-house. For watering the soil we use 

 only distilled water. 



The plants developing in sterilised soil thrive badly even in the 

 following summer, form only root hairs (see Fig. 26), and in part 

 die off. The rest of the plantlets grow on vigorously ; in the 

 summer all their roots are already provided with fungi. The 

 development of Mycorhiza is thus essential for the normal 

 development of the beech (and some other plants). 



The unfavourable result of the cultures in sterilised soil is not 

 the result of the mere sterilisation, since plants which are not 

 dependent on symbiosis with fungi (e.g. oats) are easily made to 

 flourish vigorously in sterilised soil. 



1 See Frank, Berichte d. Deutschen botan. Gesellschaft, Bd. 3 and 6. 



35. Experiments with Penicillium crustaceum. 



If we soak a slice of bread with water, place it in a glass 

 dish, and leave it under a bell-glass at the ordinary room 

 temperature, smaller forms of Mucor generally develop first of all. 



