The stereom is furnished either by cortical cells or by the tracheal elements, in a few cases by fibres which arc probably homologous with sievetubes.
E, epidermis; q, phellogen; 1, cells, and ~1, the pheliogen of the lenticel; k, cortical parenchyma, containing chlorophyll.
From the outer cortical myceliuni, again, branches pass through the epidermis and grow out in the soil, In stich cases the roots of the plants are usuall) found spreading in soils which contain a large amount of humus, or decaying vegetable matter.
The food so absorbed passes to the outer cortical mycellum, and from this tc the inner hyphae, which appear to be the organs of the interchangi of substance, for they are attracted to the neighborhood of thi nuclei of the cells, which they enter, and iii which they form agglom erations of interwoven filaments.
If a clean cut remains clean, the cambium and cortical tissues soon form callus over it, and in this callusregenerative tissuenew wood, &c., soon forms, and if the wound was a small one, no trace is visible after a few years.