THE MYXOMYCETfiS. 9l 



both ends. In Prototricbia and Enertbenema they are attacbed to 

 tbe sporangium at one end only. In Didymiiim and allied genera they 

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

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

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

 In Stemonitis and Comatricha the stem penetrates tbe sporangium, 

 forming an axis, called the columella ; in other species tbe 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 till up the interstices of the capillitium. When mature tbe 

 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 Cboudrioderma, or longitu- 

 dinally, as in P}iij.<iiruin sijutositm. In Craterium a distinct lid or oper- 

 culum is formed, and in Perichasiia tbe wall of tbe sporangium splits in 

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

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

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

 exposed, and in tbe 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 tbe Hepaticas under the influence of alterna- 

 tions of beat and moisture. In these various ways tbe spores are 

 dispersed. 



The spores are spherical, usually with a smooth, but frequently 

 with a ribbed or spiny coat. They fall into two groups as regards 

 colour : in one group the spores are dull-coloured, either brown or 

 brownish-violet, almost black ; in the other they are of a bx'igbt colour, 

 such as yellow, ochreous, red, purple, or pink. In this, as in many of 

 the lower plants, we find colour, which, in tbe higher groups, is so 

 untrustworthy, furnishing one of tbe primary bases of classification. 

 In a few genera, as Badbamia, tbe spores are at first collected in 

 groups, surrounded, according to Berkeley, by a hyaline sac ; but the 

 existence of this envelope is doubtful. 



DEVELOPMENT OF A SPOKE. 



Let us now trace the development of the spore of a typical Mj'xo- 

 mycete. When one of these is placed in suitable conditions, as in 

 water, it dehisces, and its contents pass out as a transparent, colourless 

 sphere of protoplasm, possessing sometimes a nucleus and a contractile 

 vacuole.* This remains for a time motionless, but soon we can perceive 

 little undulations of its contour, which gradually increase in extent 

 until the shape becomes elongate, and then suddenly there is developed 

 at tbe end next the nucleus a long flagellum, which flickers gently at 

 first, then more rapidly, and at last attains power enough to move tbe 

 body from its position. The object then resembles an ordinary free- 

 swimming flagellate monad. After swimming about for a few 

 hours or days it sinks to the bottom of the water, and there 



See Plate III., Fig. 6. 



