276 THALLOPHYTES. 



spores are assisted by the capillitium ; its fibres, which in the unripe condition are 

 irregularly folded, becoming straight and tense as they dry. After the rupture 

 of the sporangium-wall, the capillitium becomes exposed in many cases as an 

 extremely beautiful net- work (Fig. 197, C). The structure of the receptacles of 

 JEthalium, Spumaria, and Didymium is different. Those of J^thalium (the so-called 

 * flowers of tan') are cake-shaped, not unfrequently a foot in length and breadth, 

 and over an inch thick, but more often smaller and closely adherent to the 

 substratum (generally tan). The cake is surrounded by a brittle skin several milli- 

 metres in thickness, which is at first bright yellow, afterwards brownish, and spreads 

 itself over the substratum. The inside of this cake is composed of a dark-grey 

 easily-pulverised mass (the spores) penetrated by yellow veins, and consists of tubes 

 M'hich are interwoven in all directions and united into a net-work, but which otherwise 

 possess exactly the structure of the sporangia of Physarum, not excepting the 

 capillitium. The cortex consists of densely interwoven irregular 'bundles or of tubes 

 connected in a peculiar manner, which contain within the membrane an immense 

 number of calcareous grains (which are also found in the sporangia), as well as 

 a yellow pigment. The ^thalium-cake is therefore, according to De Bary, a tissue 

 of the tubular sporangia of a Physarum surrounded by a calcareous cortex. 



The receptacles of Lycogala epidendron bear a resemblance to those of some 

 Gasteromycetes (the Lycoperdacese). They are surrounded by a papery cortex 

 consisting of two layers. The inner layer is a homogeneous stratified light-brown 

 membrane, the outer one is much thicker and consists of a weft of branched hollow 

 fibres, the walls of which have cleft-shaped dots or are reticulate thickenings 

 projecting externally. A number of fibres of this kind penetrate into the interior, 

 piercing through the inner membrane, and form the capillitium. On the surface of 

 the structure are firm large vesicles filled with granular contents. 



The spores of the Myxomycetes, which fill up all the interstices of the 

 capillitium, resemble, from the reticulated ridges or tubercles on their surface, 

 the spores of some Tuberaceae and Gasteromycetes; but sometimes they are 

 smooth. ^ 



The spores are capable of germinating immediately after -tBeir dissemina- 

 tion ; but when kept dry they preserve this power for years. When a spore is 

 saturated with water it opens, and the whole of its protoplasmic contents escape 

 as a roundish naked mass ; but after some minutes it assumes another form, 

 becomes long and pointed at one end, where it is provided with long cilia; it- 

 has, in fact, developed into a swarm-spore, which is either endowed with rotatory 

 motion or creeps along changing its form like an Amoeba. These swarm- spores 

 multiply by division. But on the second or third day a new process begins; 

 the swarm-spores cease dividing and unite, two or more: of them coalescing- — after 

 they have gone over into the Amoeba-form — into a homogeneous protoplasmic" 

 substance, also endowed with an Amoeba-like motion^ the Plasmodium. This 

 increases, constantly absorbing into itself more swarm-spores -and coalescing with:' 

 other Plasmodia. These plasmodia now creep along the surface of the nourishing" 

 substratum (Fig. 197, A)^ and the movements are essentially similar to those of' 

 the protoplasm which circulates in the large cells of plants, but are freer and more' 

 varied. This movement in position or 'creeping ' is caused by arm-like protuberances 



