iECIDIUM. 



[ 15 ] 



iECIDIUM. 



through the orifice of the spermagonium on 

 the surface of the leaf. By a longer action 

 of moisture the jelly dissolves, and the mi- 

 nute bodies [spermatia) spread about in the 

 water exhibiting " an oscillatory motion, as 

 of a body attached at one extremity." De 

 Barv states that he found iodine arrest this 

 motion, while it persisted for some time in 

 solution of chloride of calcium. No cilia can 

 be detected. Fresh spermatia were coloured 

 bright purple red by sugar and sulphuric 

 acid, but at the same time were so acted on 

 that it could not be made out whether the}' 

 possessed a membrane free from nitrogenous 

 matter. Solution of potass renders invisible 

 the outlines, not only of the spermatia, but 

 of the sterigmata and paraphyses. The re- 

 semblance of these bodies to the spermatia 

 of the Lichens (see Lichens), is too evi- 

 dent to be mistaken; hence the same terms 

 are applied to the corresponding organs. 



Following the history of the spermagonia 

 in the plant : after the emptying of the 

 cavity, the ordinarily bright yellow or reddish 

 colour becomes dulled, all parts shrivel up 

 and form a dirtv brown mass, in which only 

 the outline of the spermagonium can be recog- 

 nized, the paraphyses become glued together 

 or fall off. The spermatia are likewise decom- 

 posed; the tough jelly spread around the 

 spermagonia preserves them for a time, but 

 they gradually vanish, until only a multitude 

 of actively moving molecules of extremely 

 small size can be detected. This mass finally 

 di'ies up, and when a number of spermagonia 

 were grouped together, a thin crust, often 

 bro^vn, is formed over the epidermis sur- 

 rounding them. 



The spermagonia occur either in regular 

 groups or scattered just like the perithecia ; 

 when the latter are on the same surface of a 

 leaf, they often form a circle round the 

 former. Frequently they burst through on 

 opposite sides of a leaf, and then the sper- 

 magonia are oftenest on the upper, the^en- 

 thecia on the lower face (PI. 20. fig. 1, sp). 



After a number of spermagonia have been 

 successively developed and discharged theii- 

 spermatia, the mycelium, from which they 

 originated, produces a new globular body 

 formed of densely interwoven filaments, 

 usually in the interior of the substance of 

 the leaf or stem, not immediately beneath 

 the epidermis, and ordinarily colourless. In- 

 creasing in size in all dhections, this 

 globular body, the perithecium, soon pre- 

 sents at its base, i. e. the point furthest 

 from the nearest epidermal surface, another 



body, composed of very numerous free- 

 ended filaments enclosed in a cellular mem- 

 brane, which body rapidly grows up within 

 the perithecium, in the dnection of the sur- 

 face of the leaf or stem. The filaments, at 

 first very delicate, are crowded very closely 

 together, and each exhibits in its interior a 

 row of short, colourless, roundish cellules, 

 the uppermost of which is always the largest 

 and the most advanced in development. 

 These cellules are the spores, and the fila- 

 ments in which they are foimd are the spo- 

 rangia or thecce. The membrane enclosing 

 the sporangia, the peridium of Persoon, 



^cidium Compositarum, Mart. 

 Fig. 5. 



Peridia in various stages of growth on the surface of a leaf : 



30 diam. 



Fig. 6. 



Perpendicular section through a burst peridium, showing 

 the sporanges contained in it: 100 diam. 



grows pari passu with them, and is com- 

 posed likewise of rows of cells, which stand in 

 a circle around the sporanges, but are firmly 

 connected together side by side by an intercel- 

 lular substance; this membrane closes in like 

 a bell or vault over the sporanges. By the re- 

 ciprocal pressure of all parts, the cells of this 

 membrane, at first spherical or ovate, become 



