ALG.E. 



[ 29 ] 



ALG^E. 



simple cellular structure met with in all 

 streams, ditches, ponds, or even the smallest 

 accumulations of fresh water standing for 

 any length of time in the open air, and com- 

 monly on walls or the ground in all perma- 

 nently damp situations. The great variety 

 of conditions of organization, all variations 

 as it were on the theme of the simple vege- 

 table cell, produced by change of form, 

 number, and arrangement of this simple 

 element, renders the Algae peculiarly inter- 

 esting as objects of microscopic research, 

 even in regard to morphological conditions 

 alone. 



This simple condition of the structures is 

 here, as in other cases, accompanied by a 

 delegation of the physiological functions 

 most completely and fully to the individual 

 cells ; that is to say, the marked difference of 

 purpose seen in the leaves, stamens, seeds, 

 &c. of the flowering plants is absent here, 

 and the structures carrying on the operations 

 of nutrition and those of reproduction are so 

 commingled, conjoined, and, in some eases, 

 identified, that a knowledge of the micro- 

 scopic anatomy is indispensable even to the 

 roughest conception of the natural history of 

 these plants. Added to this, we find these 

 plants of such simple structure that we can 

 see through, and through them while living 

 in a natural condition, and by means of the 

 microscope penetrate to mysteries of orga- 

 nization either altogether inaccessible, or 

 only to be attained by disturbing and de- 

 structive dissection, in the higher forms of 

 vegetation. 



This Class comprehends a vast variety of 

 plants, exhibiting a wonderful multiplicity 

 of forms, colours, sizes, and degrees of com- 

 plexity of structure ; but the subdivision of 

 them into three groups, characterized by 

 striking external characters, which are 

 adopted in the classifications of some of the 

 leading Algologists, facilitates the cursory 

 consideration to which we are confined here. 

 These three Orders are iheHed-spored Algce 

 (FLOBIDE^E or RHODOSPORE^E),thel)r&- 

 spored Alga (MELANOSPORE^E or Fu- 

 COIDE.S:), and the Green-sporedAlgcz (CON- 

 FER VOIDED, or CHLOROSPOREJE) the first 

 two consisting almost exclusively of Sea- 

 weeds, the last of marine and more especi- 

 ally of freshwater plants, the majority of 

 which are microscopic when viewed singly. 



The Algae are differently distributed by 

 Thuret, whose researches on their fructifica- 

 tion have thrown so much light upon this 

 class, also by Rabenhorst and Sachs, whose 



views are referred to under the Orders, and 

 VEGETABLE KINGDOM. 



Order 1. FLORIDEJE or RHODOSPORE^E. 

 Almost all marine plants, with a leaf-like or 

 filamentous rose-red or purple, rarely brown- 

 red or greenish red, thallus. Fructification 

 appearing in three forms : 1. spores, con- 

 tained in external or immersed definite 

 masses, mostly enclosed in conceptacles or 

 cystocarps (ceramidia, coccidia, favellidia, 

 &c.) ; 2. tetraspores or tetragonidia, red or 

 purple, either external or immersed in the 

 frond, rarely contained in proper concepta- 

 cles (stichidia), each consisting of a trans- 

 parent membranous sac containing, when 

 ripe, four spores ; 3. antheridia, pellucid sacs 

 filled with yellow motionless spherical cor- 

 puscles, collected in masses in situations 

 corresponding to the spore-fruits. Fertiliza- 

 tion is effected through the agency of a 

 style-like filiform process or trichogyne, 

 with which the spermatozoids copulate. The 

 trichogyne is either only the prolongation 

 of the cell in which the spores are produced ; 

 or, more generally, it is supported upon 

 small cells, which take no direct part in the 

 formation of the spores. See FLORIDE;E. 



Order 2. FUCOIDE.E or MELANOSPORE^B. 

 Marine plants with a leaf-like, shrubby, 

 cord-like or filamentous thallus, of olive- 

 green or brown colour. Fructification very 

 varied : 1. in Fucaceae consisting of mon- 

 oecious or dioecious conceptacles or oogonia 

 containing sporanges and antheridia, the 

 spores being fertilized by spermatozoids after 

 the discharge of both from the pa,rent ; 2. in 

 Laminariaceae and allied orders consisting 

 of definite or indefinite collections of 

 clavate or filiform sporanges, producing 

 biciliated zoospores, which germinate di- 

 rectly ; 3. in Cutleriacese of similar spo- 

 ranges producing zoospores, together with 

 antlieridia, like those of Fucaceae ; 4. in Dic- 

 tyotaceae presenting three forms resembling 

 those of Florideae, viz. collections of tetra- 

 spores, of sporanges containing simple spores, 

 and of antheridia. See FUCOIDE^E and 



Order 3. CHLOROSPOREJE or CONFER- 

 VOIDEJE. Plants growing in sea or fresh 

 water, or on damp surfaces, mostly green, 

 with a filamentous, or more rarely a leaf-like, 

 pulverulent or gelatinous thallus ; the last 

 two forms essentially microscopic, consist- 

 ing frequently of definitely arranged groups 

 of distinct cells, either of ordinary structure 

 or with their membrane silicified (Diato- 

 maceae). The green colouring matter con- 



