342 



BOTANY 



KK;. 267. I.eomrpt's fragills. 

 Groups of sporangia upon a 

 Moss. (Nat. size.) 



sporangia are simple and formed singly. The swarm-spores and myxamoebae of 



the Myxomycetes indicate an origin of the group from organisms resembling 



the Flagellata. 



The structure and nature of the sporangia afford the most convenient means of 

 distinguishing theditlVi - 

 ent genera. The usually 

 brown or yellow spor- 

 angia are spherical, oval, 

 or cylindrical, stalked 

 (Figs. 265, 267) or not 

 stalked (Fig. 266). They 

 usually open by the rup- 

 ture of the upper portion of the sporangium wall.-, 

 the lower portion persisting as a cup (Figs. 265 

 B, 266 A). In Cribraria (Fig. 265 C) the upper 

 part of the wall of the sporangium, which contains 

 no capillitium, becomes perforated in a sieve - like, 

 manner. In Stemonilis (Fig. 265 A) the whole peridium 

 falls to pieces, and the capillitium is attached "to a 

 collumella, which forms a continuation of the stalk. 



Plasmodiophora Brassicae ( 10 ), one of the few- 

 parasitic Myxomycetes, causes tuberous swellings on 

 the lateral roots of various species of Brassico. Its 

 multinucleate myxamoebae occur in numbers in thecells 

 of the hypertrophied parenchyma of these swellings ; 

 after the contents of the host-cell have been ex- 

 hausted they fuse into plasmodia, and these, eventu- 

 ally dividing into numerous spores, are set free by 

 the disorganisation of the plant. According to PRQ- 

 WAZEK the plasmodium first divides into unimicleatc 

 cells which then conjugate in pairs to give rise to 

 the spores ; the nuclei before the fusion have under- 

 gone a reduction division. The spores germinate like 

 those of Chondrioderma, and the myxamoebae penetrate 

 the roots of a young Cabbage-plant. The formation 

 of true sporangia, however, does not take place, and 

 this Slime-Fungus represents a more simply organised 



or, in consequence of its parasitic mode of life, a degenerate Myxomycete. 



FIG. 266. Trichia varia. A, 

 Closed and open sporangia 

 (x 6) ; B, a fibre of the capil- 

 litium ( x i!40) ; C, spores (x 

 240). 



CLASS V 

 Peridineae ( 6 - n ) 



The Peridineae or Dinoflagellata are connected as an independent and further 

 developed group with certain Flagellata (Cryptomonadinae). They occur as 

 unicellular, free-swimming organisms in fresh water, but for the most part in the 

 sea where, together with the Diatomeae, they constitute an important constituent 

 of the plankton. Their cells are characterised by the possession of two long cilia 

 or flagella which spring from the middle of the ventral surface in a longitudinal 

 furrow ; one of the cilia is directed backwards, the other is thrown into t-urvt- .-tin I 



