ALGAE. CONFERVOIDEAE. 47 



by intermediate forms ; one extreme is exemplified in C. divergens^ which as it de- 

 velopes from the spore produces at first irregularly branched, creeping, segmented 

 filaments, from which spring ascending branches that are also irregularly branched and 

 segmented ; the thallus has no definite form. C. pulvinata, on the contrary, has the 

 shape of a hemispherical cushion ; the segmented filaments which are the result of 

 germination branch in one plane somewhat irregularly, but on the whole taking the 

 form of a disk ; from them rise ascending, articulated branches, which are themselves 

 again branched, and form the cushion. In the following species there are no ascending 

 branches, but the others, which cling closely to the substratum, form a more or less 

 regular disk, as in C. irregularis, where irregular ramifications lying in one plane 

 fill up by degrees all the intervals, so that a layer of cells is formed almost without 

 interstices ; on the other hand, in C. soluta (Fig. 23) dichotomous branching with 

 corresponding cell-division begins in the two first daughter-cells of the germinating 

 spore, so that a complete disk is early formed with radial bifurcations, which either 

 lie loosely beside each other or are packed closely together. In the above species the 

 branches arise laterally from cells of the thallus, never from the terminal cell of a branch ; 

 in C. soluta dichotomy appears with the regular disk-like centrifugal growth, and this 

 structure reaches its highest perfection in C. scutata ; the first cells produced in ger- 

 mination remain laterally connected from the beginning and do not form isolated 

 branches ; the young circular disk enlarges by growth at its circumference, the marginal 

 cells dividing by radial and tangential walls. This growth may be reduced to the 

 type of the foregoing ; the primary laterally united branches grow out radially with 

 equal rapidity and become segmented by transverse walls (here tangential), whilst the 

 expansion of the terminal cell of each radial row with its consequent radial segmen- 

 tation corresponds with a dichotomy. The prevailing rule in the previously mentioned 

 species, that only the terminal cell of a branch is divided by transverse walls, finds its 

 expression in C. scutata in the marginal cells only of the disk being divided by tangential 

 walls. 



The reproduction of Coleochaete is effected by asexual swarm-spores and by 

 sexually produced resting oospores. The oospores do not produce new plants 

 directly, but several swarm-spores. The alternation of generation is as follows : the 

 first swarm-spores, which issue on the commencement of vegetation in spring from 

 the cells of the oospore-fructifications of the preceding year, produce only asexual 

 plants, -that is plants which produce only swarm-cells ; after a longer or shorter series 

 of asexual generations there arises a sexual generation which is either monoecious 

 or dioecious according to the species. One oospore is produced by fertilisation in the 

 oogonium, and is enclosed in a peculiar cortical layer of cellular tissue ; the oospore 

 developes into a fructification formed of parenchymatous tissue, and from its cells the 

 first swarm-spores issue forth in the next vegetative period. Swarm-spores (Fig. 

 24, D) may be formed in any vegetative cell of the Coleochaeteae, but in C. pulvinata 

 chiefly in the terminal cells of the branches. They are always the product of the whole 

 of the contents of the mother-cell, and escape through a circular hole in the cell-wall. 

 The oogonium is always the terminal cell of a branch, in C. scutata therefore 

 the terminal cell of a radial row (Nageli). The details of its formation are 

 liable, according to the growth of the plant, to many though subordinate modi- 

 fications. We will examine these details more closely in one species, C. pulvinata 

 (Fig. 24). The terminal cell of a branch swells out and elongates at the same time 

 into a narrow tube (pg to the left in A), which then opens (og" to the right in A] and 

 emits a colourless mucilage. The protoplasm of the swollen portion of the cell con- 

 tains chlorophyll and forms the oosphere, in which a nucleus is visible. Antheridia are 

 formed at -the same time by the outgrowth in adjacent cells of two or three protu- 

 berances from each (an in A), which are separated off by trans verse- walls ; each flask- 

 shaped cell thus formed is an antheridium, and its entire contents form a spermatozoid 

 (*) of elliptical shape and with two cilia, which moves about like a swarm-spore; its 



