72 TRANSACTIONS AND PROCEEDINGS OF THE [Sess. Lxn. 



nitrates are found as a constant constituent. Eeeent 

 researches have shown that the nitrogenous matters in the 

 soil, which are chiefly there in the form of albuminoid 

 substances — the residues of former plants — are, in the 

 process of decay, converted into ammonia salts, and these 

 again into nitrates, through the agency of various bacteria 

 inhabiting; the soil ; and that these ors;anisms are so abundant 

 and, in ordinary circumstances, so active that all nitrogenous 

 matters which have become soluble in the soil are ultimately 

 converted into nitrates, and that in that state they are 

 absorbed by the roots of plants, and by means of proper 

 chemical tests their presence can be detected. 



Professor Frank observes that in the roots of trees or 

 other plants affected by the mycorhiza he has not 

 succeeded in finding nitrates, and this would seem to 

 show that these roots are receiving their nitrogen from 

 the mycorhiza in the condition of nitrogenous organic 

 substances, viz. of elaborated organic matter such as is 

 found in humus. It may be objected to the symbiotic 

 theory that conifers and cupulifer^e can be grown in soil 

 containing no organic matter. That is quite certain, and 

 Professor Frank gives details of many experiments where 

 trees of these orders were planted in sandy soils containing 

 no mycorhiza both in pots and in the open, and in such 

 cases no mycorhiza appeared upon the roots of the plants. 

 They had the characters of normal roots, provided with 

 hairs like the roots of other plants, and capable of taking 

 up the solul)le mineral matters contained in the soil. But 

 he found that in such cases the plants, if they did not die 

 down, maintained a sickly growth, which contrasted strongly 

 with that of plants sown or planted under similar con- 

 ditions, with the sole difference that they were supplied 

 with humus in which the hypha3 of the mycorhiza wen; 

 abundant. 



The Ijenetit that forest trees derive from the accumula- 

 tion at their roots of the dead leaves and vegetable debris 

 shed from a])Ove is known to all foresters, and also the 

 injurious effects whicli follow the removal of this vegetable 

 matter. It had hitherto been supposed that the benefit the 

 roots derived from the covering of decaying vegetable stuff 

 was simply that of protection against extremes of heat and 



