ly. rUCACE^. 61 



branches or leaves, which then become succulent and full of slimy mucus ; and in 

 the highest types, small metamorphosed branchlets are from the beginning set apart 

 as organs of fructification. These metamorphosed branchlets, or the swollen parts 

 of ordinary branches which are filled with spore-cavities, are called receptacles ; 

 {receptacula, Ag. — Endl. — carpomata^ Kiitz.) 



Each spore cavity, placed immediately beneath the outer wall of the frond, and 

 communicating freely with the water through its pore, is a hollow, spherical, 

 membranous, bag-like chamber, whose inner surface is clothed with pellucid hairs 

 (jMranemataJ, among which organs of fructification of two kinds (male? and 

 female) are placed. Sometimes both kinds or sexes are found in tlie same cavity ; 

 sometimes all the cavities of one plant produce one kind only, and all those of 

 another plant the other kind. (A vertical section of one of the female spore-cavities 

 of Fucus furcatus, figured at our Plate III. A, fig. 4, will show the general appear- 

 ance of the fructification.) 



The sfjores are lodged within colourless, glassy perispores, or large, swollen) 

 membranous, closed cells, attached to the walls of the cavity ; each perispore 

 containing from one to eight, and most commonlj^ four spores. The perispore 

 originates, like the hairs or paranemata, from the wall of the cavity, and appears 

 to be formed from one of these hairs, which, having been fertilized at an early 

 period of its development, instead of continuing to grow by the production of new 

 cells at its apex, like an ordinary hair, has been arrested at the first or second cell ; 

 and this cell, becoming enlarged, has an endochrome gradually elaborated within 

 it, and finally either condensed into a single spore or divided into several. In an 

 early stage the colouring matter, or endochrome, is of a very fluid substance, and 

 pale olive hue. Gradually it becomes darker and more opaque, its particles lying 

 closer together, and at length is partially solidified and invested with a delicate 

 membranous envelope, which constitutes the testa of the spore. In Halidrys, 

 Cystoseira, and several other genera, each perispore contains at maturity but a 

 single spore ; in Fucus and others, the number of spores varies from two to eight, 

 or perhaps a larger number. 



The paranemata are either simple or branched. Those which produce Antheridia 

 are always branched, and the antheridia are formed from the terminal cell of each 

 branchlet, which is enlarged and ovate, obovate, or club-shaped. This Antheridium, 

 or supposed male, is a pellucid, enlarged, closed cell, containing a multitude of 

 minute corpuscles (sporicUa, Ag.), which are supposed to represent the pollen, if not 

 to fulfil its office in fertilizing the spore. They are oval, somewhat pointed at one 

 end, and contain a reddish-orange granule ; and they are furnished with two 

 extremely slender vibratile hairs or cilia, one of which issues from the narrow 

 extremity of the corpuscle ; the other, which is of greater length, from the coloured 

 granule. The corpuscles, at first contained within the antheridium, at length issue 

 from it, escaping into the surrounding water, and immediately commence a suc- 

 cession of rapid movements to and fro, and in circles and curved lines, strikingly 

 similar to the ciliary movements of some of the Infusoria, or of the spores of 

 some of the fresh water Alga3 of the Green series. These movements depend on 

 the rapid vibrations of the cilia. During progression, the narrow end of the cor- 



