1 6 FIRST GROUP.— THALLOPHYTES. 



vegetative stage before proceeding to the formation of its fructification, which takes place 

 in the following manner. A number of cells arise by free cell-formation in the middle of 

 the roundish plasmodium ; these cells become invested with cellulose and unite to form 

 a column or stalk of parenchymatous tissue in the interior of the plasmodium at right 

 angles to the substratum. While this column increases constantly in height, the 

 surrounding protoplasm creeps up it and collects at its summit into a round mass, the 

 whole substance of which now breaks up into numerous spores. Here we have the 

 course of development of a Myxomycete in its simplest form. In most other cases the 

 development is more extended and more complex, though the mode of its commence- 

 ment is essentially the same in all the Myxomycetes. The spores produce from one to 

 eight swarm-cells, which eventually become amoeboid bodies, grow and multiply by 

 repeated division, and finally unite together in large numbers and form plasmodia. 

 But the Plasmodia of other Myxomycetes do not proceed at once to the formation of 

 fructifications, but maintain an independent life for a longer period, creeping into the 

 moist cavities in their substrata, like the yellow plasmodia inside tan which come at 

 last to the surface, and there run together into large flat cakes known as 'flowers of tan.' 

 Other Plasmodia creep about for some time in rotting wood or among decaying leaves, 

 and at length come to the surface, where they usually form a number of fructifications all 

 at once. Fig. 7 A will give some idea of the way in which the movements of the plas- 

 modia produce reticulated forms. The mass of the plasmodium, which is granular and 

 watery within and bounded on the outside by a skin of homogeneous protoplasm, is 

 perpetually changing its shape ; protuberances are formed at various spots in its 

 circumference, which glide and creep with a forward movement, and ramify and 

 anastomose with one another, while the substance of the plasmodium moves after them 

 from behind, and thus causes the whole body to advance slowly in a given direction. 

 Just before fructifications are formed the plasmodia show a tendency to creep up upright 

 bodies, and thus the fructification is often found on plants, stems and leaves at a con- 

 siderable distance from the original nutrient substratum. With a view to fructification 

 the Plasmodium collects at certain spots, and forms either a broad cake, as in ' flowers 

 of tan,' or weak ascending outgrowths, which gradually assume the form of the typical 

 fructifications, usually that of a stalked spherical or club-shaped body or a winding tube^ ; 

 these changes of form are usually completed in a few hours. It has already been 

 observed that the ripe fructification is usually invested with a firm membrane, and 

 that a so-called capillitium is often formed inside it with numerous spores lying in its 

 interstices. Neither the wall of the fructification, nor its stalk which is usually hollow, 

 nor the capillitium are formed of cehulose ; we must suppose that the substance of the 

 Plasmodium, after it has assumed the outline of the fructification, becomes differentiated 

 into two substances, one of which is hardened into membranes, tubes and solid threads, 

 and so forms the stalk, the wall of the fructification and the capillitium, while the rest 

 of the protoplasm retaining the power of further development breaks up into small 

 rounded portions, which invest themselves with cell-walls and thus form the spores. 



The protoplasm, in becoming differentiated into spores and parts incapable of further 

 development (wall of fructification and capillitium), also gets rid of other portions 

 of its contents which are of no use in reproduction, and especially of the lime, which 

 is eliminated in large quantities in the form of a finely granular carbonate, and of the 

 yellow substance which covers the fructifications of ' flowers of tan ' with loose flakes. 



The Myxomycetes can pass from all the states of movement to states of rest, in 

 which they are able to bear unharmed the effects of desiccation. The motile cells 

 become rounded and encysted, that is they clothe themselves with a membrane which 

 they abandon when they recover their power of movement under the proper conditions 

 of moisture and warmth. Small plasmodia also become encysted. Larger plasmodia 



^ Rostafinski gives the name of '■Aethalium ' to large fructifications which are produced by the 

 coalescence of several simple ones, and which are therefore syncarps, as in ' flowers of tan.' 



