32 



EVOLUTION OF PLANTS 



active movements and other evidences of life (Fig. 4, A). 

 The Monera are aquatic, often parasitic, organisms and 

 their life-history is a simple one. After the plasmo- 

 dium has reached its maximum size it contracts and 

 develops a firm covering and the contents of this cyst 



divide into a great many 

 parts, each of which is pro- 

 vided with a nucleus. These 

 minute nucleated masses es- 

 cape in the form of actively 

 swimming bodies which may 

 form a new plasmodium by 

 simple growth ; but some- 

 times, by the fusion of a 

 great number of the sepa- 

 rate spores, as in Protomyxa, 

 a large plasmodium may be 

 formed at once. 



In the Mycetozoa, or Slime- 

 moulds, which are often re- 

 garded as plants, the life- 

 cycle is somewhat more 

 complicated, due to the fact, 

 perhaps, that they are terres- 

 trial in their habits. The 

 active condition in these is 

 also that of a plasmodium, 

 these naked masses of white or yellow slimy matter 

 often reaching a large size. The commonest of these 

 is one found growing upon old tan-bark where the light- 

 yellow soft mass may often be met with in damp, cloudy 

 weather, the plasmodium shunning too strong lights 



FIG. 4 (Mycetozoa) . A, a Slime- 

 mould growing upon a bit of 

 rotten wood ; B, two of the 

 fruiting structures (sporan- 

 gia) of another form (Stem- 

 onitis) ; C, two ripe spores of 

 Trichia ; D, the active mo- 

 tile protoplasmic mass which 

 escapes from the spore when 

 it germinates ; /, the flagellum 

 or motile organ ; n, the nu- 

 cleus ; E, two amoeboid later 

 stages which have lost the 

 flagellum and later unite 

 with others to form the larger 

 "plasmodium," shown in A. 

 v, the contractile vacuole. 



