214 Transactions British Mycological Society. 



depth of 1-5 to 2*5 inches. The roots were growing in a series 

 of layers, one below the other, the number in each series de- 

 pending upon the thickness of the accumulated leaves. The 

 upper layer is, as a rule, the best for illustrative purposes. 



Any hypothesis advanced respecting the exact relation that 

 exists between the root of the tree and the fungus must take 

 into consideration the fact that the bulk of the mycorrhiza 

 met with in woodlands is formed among decaying leaves, of 

 which the progress of decay is not greatly advanced, and also, 

 that mycorrhiza is abundant a very short distance below the 

 surface of the leaf mass. 



The above statements are emphasised because, during a period 

 of drought even of short duration, the conditions, represented 

 (figs. I, 2 and 3) as normal, are completely changed by the 

 mycorrhiza being desiccated and thereby killed. 



Mycorrhiza does not revive after being destroyed by the lack 

 of moisture and does not reappear on the return of copious rain 

 until new rootlets have been developed and they in their turn 

 have become associated with a fungus. 



Provided a drought is not sufficiently prolonged to destroy 

 the thicker roots, on which are the finer ramifications, new 

 fibres are produced in abundance, on the return to normal 

 atmospheric conditions, among the same leaves where mycor- 

 rhiza formerly existed and where fresh fungus mycelia have 

 already appeared. No evidence has been observed of any 

 tendency on the part of newly formed rootlets to avoid fungus 

 hyphae, with which they soon become associated. A root- 

 system is developed and spreads through the leaf-masses where 

 fungus mycelia are abundant. In the case of roots that enter the 

 lower layers of a moss carpet there is indication of a definite 

 tropism as the moss forms a nidus for numerous fungi and roots 

 turn upwards from the soil into it and subsequently develop 

 mycorrhiza. 



In the field, the collector needs very little special apparatus. 

 A scout's knife, test-tubes of one inch diameter or bottles of 

 2 oz. capacity, a pocket lens and the ordinary vasculum are 

 all that are required. On no account must the material be exposed 

 for even a short period to a dry atmosphere. The test-tubes or 

 bottles should be filled with water for examination and for 

 safe transport. On placing a portion of mycorrhiza in a tube of 

 water, it is possible to determine with a pocket lens the form, 

 colour, and general appearance which may be wax-like or 

 shaggy; points which must be taken into account when deciding 

 whether to keep or to reject material. 



The mycorrhiza of beech in situ (fig. i) shows (i) the horizontal 

 growth of roots through a loose layer of leaves which are in an 



