66 



SLIME MOULDS AND THEIR ECONOMIC IMPORTANCE. 



By J.W. EASTHAM, Chief Assistant Botanist, Central Experimental 



Farm, Ottawa. 



The Slime Moulds ( Myxomycetes or Mycetozoa ) are a group of 

 organisms not so well known as the}- deserve to be to students of plant 

 life. The delicacy and variety of their fruiting stages will well repay 

 study on the part of anyone possessed of a microscope or even of a good 

 pocket lens, while in their life history they show a most cur- 

 ious succession of phases and oiffer to the Biologists a presen- 

 tation of the question "What distinguishes a plant from an 

 animal?" in a form which has as\ yet eluded a satisfactory answer, xne 

 scientific names applied to the group are in fact indications of this ignor- 

 ance on our part of their true nature, for the name Myxomycetes m^eans 

 "Slime-fungi" and that of Mycetozoa is literally "fungus animals". The 

 former term accords with the view that these organisms are 

 plants, the latter wdth the opinion that they are to be considered of the 

 natiure of animals. Both names suggest a close relationship with the fungi, 

 and they will usually be found classed with this group in the larger sys- 

 tematic works, although fungi in the strict sense they certainly are not. 

 It may perhaps suffice for our purpose if we say thait they are organisms 

 possessing at different stages of their history some of the well-marked 

 attributes of plants and animals respectively, but in their mature form 

 at any rate showing on the w^hole a closer relationship with the former 

 than ^vith the latter. 



The life history of a typical slime-mould is briefly as follows: — As in 

 the case of most of the simplest plants reproduction is effected by spores. 

 These are produced in great numbers, are generally spherical, and have a 

 typical vegetable characteristic in that the wall or containing membrane 

 of each spore is composed of cellulose. Under suitable conditions, prin- 

 cipally a slight amount of warmth and moisture;the spores germinate;, the 

 ■wall cracks and the living protoplasmic contents of the spore slips out 

 into the surrounding water as a minute colorless body of indefinite form. 

 It possesses a considerable degree of activity, creeping along by the pro- 

 trusion of certain portions of its substance or swimming along through 

 the water, being in the latter case piopelled by whip-like lashings of a de- 

 licate thread of protoplasm pushed out at one end. At this stage the 

 organism bears a very close resem.blance to some of the simplest animals 

 and hence it is termed a "zoospore" or "animal-spore." The zoospores 

 may m.ultiply by the simple process of each dividing into two, but ulti- 

 mately, however, a number of them come together and coalesce almost 

 like so many drops of ^vater, forming a large protoplasmic mass termed 

 a Plasmodium. This plasmodium rapidly increases in quantity- -one 



can hardly say size — feeding on solid' particles of vegetable debris. These 

 are taken into the substance of the plasmodium and then digested which 



