INTRODUCTION TO CRYPTOOAMIC ROTANY. 387 



the cavity. Beauty of form is, moreover, often combined with 

 exquisite colouring, which is sometimes brilliantly metallic, 

 exhibiting tints of steel, gold, copper, or silver, and sometimes 

 vying with precious stones.* In a multitude of species 

 there is a well-defined stem, which may either spring directly 

 from the matrix, or from a membranous exj^ansion, the 

 remains of that part of the original pulpy matter which was 

 not developed into peridia. In these cases, the rupture some- 

 times takes place with a regular horizontal fissure, so as to 

 present the appearance of a little cup with a convex or flat lid, 

 often of a chalky aspect. Sometimes the membranous portion 

 of the peridium separates half way down, as in Cribraria (Fig. 

 75, h), the upper portion consisting of curiously branched veins, 

 through the interstices of which the spores escape ; and 

 sometimes, as in Dictydium, the membranous coat vanishes 

 through the whole course of the peridium, leaving behind a 

 variously reticulated balloon, which is often umbilicated above 

 or below, so as to present an exquisite object under a low 

 magnifier. The peridium consists of one or two membranes. 

 In Fhysarum there is but one, which is, for the most part 

 perfectly smooth, and often showing the most brilliant pris- 

 matic or metallic tints ; in Diderma, they are perfectly distinct 

 and separate, more or less completely, from each other ; while 

 in Didyniium, the outer coat assumes various forms, being 

 floccose, furfuraceous, or squamose. 



363. The flocci again exhibit as various differences as the 

 other elements. In some cases they are equal in length 

 throughout, variously branched, sometimes attached to the 

 walls, sometimes to the columella. In Arcyria, they form a 

 beautiful elastic network, which is greatly elongated on the 

 rupture of the upper part of the peridium. In some cases the 

 threads are in parts, especially where they branch, much flat- 

 tened, and form triangular or multangular expansions, with 

 occasionally a central cavity resembling an intercellular space ; 

 a structure which also obtains in the veins which traverse 



* Very thin dry membranes in the animal kingdom .sometimes ex- 

 hibit such tints. 1 have a pear-leaf studded with the eggs of some moth, 

 the substratum of which is beautifully prismatic. 

 22 



