In the famous dedicatory letter of his Alceste he mentions among other conceptions on which his reform of opera was to be based, that the co-operation of the instruments ought to be regulated in proportion to the interest and the passion, a doctrine of which the true significance lies in its connexion with other conditions of opera which are incompatible with the polyphonic treatment of instruments as threads in a decorative scheme.
In the bulky forms colorless branches frequently grow out from some of the cortical cells, and, pushing among the already-formed threads in a longitudinal direction, serve to strengthen the thallus by weaving its original threads together.
A nervous system has been shown to exist in many species, and consists of a perioesophageal ring giving off usually six nerves which run forwards and backwards along the lateral and median lines; these are connected by numerous fine, circular threads in the sub-cuticle.
In all cases, while the internal threads which bear the cortical branches consist of elongated cells with few chromatophores, and no doubt serve mainly for conduction of food substances, the superficial cells of the branches themselves are packed with chromatophores and form the chief assimilating tissue of the plant.
The simpler Fungi, like the simpler Green Algae, consist of single cells or simple or branched cell-threads, but among the higher kinds a massive body is often formed, particuTissue t~Jf larly in con nexion with the formation of spores, and, er~n,~,onthiS may exhibit considerable tissue-differentiation.