96 



SYMBIOSIS. 



in Monotropa. The root-system of a tree has not only to secure 

 nourishment, but also the rigidity and stability of the tree.^ 

 This latter can only be attained by a wide distribution of roots 

 in the firm subsoil free from humus, where normal roots with 

 root-hairs will be formed. The nursing function of the mycorhiza 

 seems thus to be less important than in the case of Monotropa. 



Fig. IS. — Mycorhisa of Pi7ius Cemi/ra. .^, Typiciil mycorhiza. £, Root showing 

 clusters of mycorhiza as well as portions clad with ilne root-hairs. C, Rootlet 

 exhibiting button-like thickenings externally devoid of a fungoid mantle, but 

 internally completely destroyed by mycelium. D, Section through a thickened 

 branch of a mycorhiza-cluster : a, fungoid mantle ; 6, fungoid tissue between 

 the cells of the root, rendering them unrecognizable except by their large nuclei ; 

 the inner parts contain no fungi, (v. Tubeuf del.) 



My newest investigations on this subject ^ show that, amongst- 

 the gymnospermous forest-trees, the Abietineae alone have roots 

 externally clothed with a fungus ; the remaining groups have 

 all endophytic mycorhiza. The Abietineae have frequently only 

 a fine mantle of fungus on their rootlets, and do not produce the 

 tufts of short, branched roots so characteristic of mycorhiza in 

 general. Frank does not seem to -be altogether correct in his 

 view that the Abietineae are almost or quite incapable of multi- 

 plication by slips, because they would then require to exist for a 

 time without mycorhiza. Probably there is some other reason 

 for this, because the Salicaceae (e.g. Poplars), which have typical 

 coral-branched mycorhiza, are almost exclusively multiplied by 

 slips. 



^Hoveler, ("iib. die Verwerthung d. Humus bei d. Emahrung d. chlorophyll- 

 fuhrenden Pflanzen." Inaug. Diss., Berlin, 1S92), states that roots are able to 

 utilize the soil-constituents without aid of fungi. 



^ Tubeuf; Forst. -iiaturwiss. Zeituchri/t, 1 896. 



