390 ORGANOGRAPHY. 



transitory stnictures; when discharged from the parent-cell they 

 either make their way to a germ-cell of a spore, fertilize it and 

 disappear; or if debaiTcd from this, at once perish without ger- 

 mination." 



Besides the above-mentioned reproductive organs, there have 

 been found in certain genera of this order — sporangia, in which 

 resting-spores are produced by impregnation from spermatozoids 

 derived from anther idia. 



2. RhodosporecB, Floridea, or Rose-coloured Alga. — There 

 appear to be three forms of reproductive sti-ucture in plants of 

 this order of Algre ; these are termed respectively 1. tetra- 

 spores; 2. spores; and 3. antheridia. The tetraspore is a pecu- 

 liar feature of the plants of this order, and at once distinguishes 

 them from their allies. The sexual nature of Rhodosperms 

 would appear to be tolerably well ascertained. 



1. Tetraspores. — These are either naked, as in Callithamnion, 

 and then either situated on the outside of the frond, or more fre- 

 quently collected in masses and immersed in its substance 

 (^Jig. 831); or they are collected together in distinct organs of 

 varying forms, called conceptacles ^ (fig. 832), and stichidia {fig. 

 833). The tetraspore consists of a more or less globular trans- 

 parent sac or cell, called the perispore, which when mature 

 contains within it four, (or rarely three), sporulcs (fig. 831). 

 The occurrence of three sporules was formerly considered to be 

 tolerably frequent, but this is now known to be an error; the 

 fourth sporule is however occasionally suppressed, as in Lepi- 

 dosirohus, as first shown by Mr. BroAvn. The tetraspores are re- 

 garded by Harvey and some other authors, as analogous to 

 gonidia. 



2. The Spores, like the tetraspores, vary in their situation. 

 Sometimes they are collected together in masses without any 

 special sac: but generally they are situated in distinct hollow 

 conceptacles, which have received different names, according to 

 their structure and arrangement; the tQvms fat'ellce (fig. 834), 

 ceramidium (fig. 835), and coccidiuvi are those which are most in 

 use. The spores are generally formed by the transformation of 

 the cells of articulated threads, situated commonly in the concep- 

 tacles. They consist of at least two coats of a somewhat gela- 

 tinous natm'c, enclosing a dense clustered granular mass. 



3. The AvOuridia. — But little is known of the structure of 

 the antheridia of this order of Algjc. They arc collections of 

 little cells of various forms, and variously arranged, in each of 

 which a peculiar l»ody, called a spermatozoid, is ultimately formed. 

 According to lierkley, " the s])ermatozoids vary a little in shape. 

 Derbies and Sober figure many of them with a delicate append- 

 age; but Tliuret lias in vain sought for such an aj)]>carance. 

 There can, however, l)c little doubt but that they are truly im- 

 prcgnatory organs. The tlagelliform api»endage cannot certainly 



