586 PROGRESSIVE STAGES IN COMPLEXITY OF STRUCTURE. 



the sclerotia correspond to the single masses of protoplasm from which the whole 

 mass had previously been formed, and that these have not surrendered their 

 individuality, although their boundaries cannot be recognized in the mass. The 

 unions of fused masses of protoplasm devoid of cell-wall are inconsiderable in 

 number in comparison with the enormous quantity of those combinations in 

 which each portion of protoplasm is surrounded by a cell-wall, by means of 

 which the cohesion of the whole is brought about. The latter are classed as 

 cell-complexes or tissues and are for the sake of clearness divisible into four 

 groups, which may be distinguished as rows, nets, plates, and masses. 



Its name tells us what a filamentous cell-complex looks like. As regards 

 its production, it is to be noticed that the partition-walls, which are formed by 

 the segmentation of its cells, always stand at right angles to the long axis of 

 the cell-filament, and are therefore parallel to one another. The general appear- 

 ance of this tissue is regulated according to the particular shape of the single 

 ceUs. If the individual members of the row are spherical, chain-like strings 

 of pearls are produced, such as are found in the Nostocacese; if the individual 

 cells are cylindrical, long or short, then thread-like structures arise from their 

 end-to-end arrangement, as may be frequently observed in the Zygnemese and the 

 CEdogonicEe. If the cylindrical cells decrease in thickness as the filament 

 increases ia length in one direction, whip-like forms arise, as, for example, in 

 the species of the genus MastichoncTna. Occasionally the single members of 

 the row are tabular, and the tablets are joined to one another by their narrow 

 edges, in which case ribbon-like rows are produced, as in Odontidium; or the 

 neighbouring tabular cells are only connected by their corners, in which case 

 the row has a zigzag appearance, as in the genus Diatoma {c.f. vol. II. fig. 369 ^'). 



In the reticular cell-complexes the numerous cells are seen to be so arranged 

 that they adjoin one another by comparatively small contiguous surfaces, 

 joining together at two or three, more rarely four, angles of corresponding size. 

 The partition - walls intercalated during the division are not all parallel with 

 one another, but are arranged in more than one dimension of space. Nets 

 may be distinguished as O'pen and closed. In the former, which may be best 

 compared with the net-work of rivers on a map, the cells only seldom form 

 closed meshes, but start out from one another like the prongs of a fork. Open 

 nets occur very often, especially in the mycelia of fungi, in species of the green 

 Confervoidcce living in water (Cladophora and Ghaetophora) and in numerous 

 red Floridese. Much rarer are the closed nets with hexagonal meshes, as, for 

 example, those of the Water-net (Hydrodictyon) described on p. 36, and the 

 remarkable nets of Volvox globator, comparable to hollow spheres, which were 

 considered on p. 37. Open reticular cell -complexes permeate the decayed 

 trunks of trees, the mould of the forest-soil, and the humus of the meadow- 

 ground. Here they exist as saprophytes, or on living plants and animals as 

 parasites ; or they are only attached by a few cells to the substratum, and the 

 forked ramifications stretch out from these starting-points like fans and radiate 



