7G THE MYXOMYCETES. 



size, from a little rounded heap just visible to the naked eye, to a mass 

 two feet lonj,' and an inch or more thick. This sporangium may have 

 one or more walls, either of which may contain a deposit of lime — 

 usually, it is said, in the form of oxalate — either in thinly-scattered 

 crystals or granules, or foi'ming the greater portion of its substance. 

 The walls of the sporangium and the stem are destitute of proper 

 cells : they are often composed of a delicate homogeneous membrane, 

 or only bear a few thickenings on the surface in cei'tain forms peculiar 

 to the different species. The stem often springs from a sinall patch of 

 a similar homogeneous substance, called the hypothallus, by which it 

 is attached to the matrix. 



The contents of the sporangium most often consist of a vast number, 

 sometimes millions of millions,* of spores, amongst which there is 

 present, in addition, a structxire called the capillitium : in a ^'ew cases 

 the capillitium is apparently wanting. The capillitiuni is composed 

 of threads, sometimes simple, sometimes branched : sometimes fi-ee, 

 sometimes combined ; in one species formed of delicate tubes with trans- 

 lucent walls, in another furnished with spiral markings or ridges or 

 spines projecting from their outer surface ; sometimes containing air, 

 and at other times tilled with lime. In many cases, also, the knots or 

 points of junction of the threads are enlarged, and these knots may, 

 or may not, contain lime. The mode of attachment of the capillitium 

 is also extremely varied. In Trichia the threads are perfectly free at 

 both ends. In Prototrichia and Euerthenema they are attached to 

 the sporangium at one end only. In Didymium and allied genera they 

 are arranged radially. But in the majority of the species they form 

 a more or less complicated network, in which a few of the ends may be 

 free, while most of them are attached to the wall of the sporangium. 

 In Stemonitis and Comatricha the stem penetrates the sporangium, 

 forming an axis, called the columella ; in other species the columella 

 is the swollen summit of the stem, or merely a denser portion of the 

 capillitium ; in some it is altogether absent. The spores in all cases 

 densely fill up the interstices of the capillitium. When mature the 

 sporangium dehisces either irregularly, as in Trichia, or radially, 

 forming segments which curl back like those of a Geaster, or the 

 petals of a flower, as in some species of Choudrioderma, or longitu- 

 dinally, as in rinjsarum sinnosum. In Craterium a distinct lid or oper- 

 culum is formed, and in Perichaena the wall of the sporangium splits in 

 a circumscissile manner, like the capsule of the Henbane or Field 

 Pimpernel. Oftentimes the upper portion of the wall of the sporan- 

 gium splits off in minute fragments, and the capillitium is left 

 exposed, and in the case of Arcyria its elasticity causes it to enlarge 

 to several times its original size. The spiral threads of Trichia twist 

 about like the elaters of the Hepatio£B under the intiuence of alterna- 

 tions of heat and moisture. In these various ways the spores are 

 dispersed. 



* I have calculated, from measuremonts, the number of spores in one sporan- 

 gium of Comatricha tijphina; there were at least one thousand millions. The 

 number in an a'tlialiuiu ol' Itctifuliiria or Fulij.'o nuist he enormously greater. 



