PREFACE TO THE ENGLISH EDITION xi 



study to the student of botany as calculated both to test his 

 knowledge in other departments of his science and to open 

 out new lines of thought as he considers the interactions 

 between one plant and another, and between both and other 

 factors living or not of the environment. 



Hartig's ingenious explanation of the spread of the well- 

 known Larch-disease may or may not be accepted in all its 

 details, on the evidence given, and dissent from his explanations 

 of such diseases as " Canker," &c., has been expressed, but I 

 would maintain apart from my acceptance of the general truth 

 of his arguments that they teach the student very clearly how 

 to investigate and think out these complicated matters for 

 himself. 



We are still decidedly wanting in information concerning 

 many diseases of trees. Standing elms and other trees are 

 occasionally found in this country with a species of Hymeno- 

 mycete growing from the trunks six feet or more above the 

 ground : are these parasitic or not, and what is their mode of 

 action ? How does Poly poms squamosus attack timber ? What 

 are the exact biological relations of Polyporus fomentarius, 

 Fistulina hepatica, and a number of other forms found in this 

 country, to the trees on which they grow ? 



These and numerous other questions await solution, by means 

 of thorough investigations properly conducted in this country, 

 along such lines as Hartig has laid down in Germany, and it 

 should be borne in mind that such studies offer stores of facts 

 likely to be of the utmost interest to investigators in other 

 branches of Botany. To give one instance only : the study 

 of the destruction of the walls of the tracheids, and other 

 elements of which timber is composed, by the hyphae of fungi, 

 shows that there is considerable variety in the processes of 

 piercing, delignifying, corroding, and dissolving them, and it 

 seems a safe conjecture that valuable information as to the 

 intimate structure of these walls may be derived from the 

 examination of the way the fungus unbuilds them, so to 

 speak. 



