248 



METAMORPHOSIS 



In the second state no vital phenomena are manifested, neither growth nor 

 absorption of food ; though completely desiccated, the protoplasm retains its 

 capacity for forming a plasmodium for months or even for years. We may 

 regard the plasmodium as the vegetative, the other we term the reproductive 

 stage of the fungus, or we may speak of it more definitely as the ' sporangium ' 

 and describe the cells within it as spores. These spores preserve the character- 

 istics of the slime fungus at a time which is unfavourable to vegetative life — 

 they propagate the organism. The questions we have to ask and, as far as 

 possible, to answer are : — What are the factors which induce the appear- 

 ance of the vegetative and what of the reproductive state ? What significance 

 lies in the fact that the former state is destitute of definite shape and that the 

 latter has a constant shape ? 



As our second example we will select a fungus, found in the frog's excreta, 

 and belonging to the Entomophthoreae, viz. Basidiobolus ranarum. It is 

 a heterotrophic plant, requiring organic as well as inorganic nutritive materials. 

 For this fungus, as for many others, peptone and sugar form an excellent 

 culture medium ; peptone alone, however, will serve quite well. The usual form 

 of a Basidiobolus is a cylindrical cell many times longer than broad. The proto- 

 plasm is never naked but is always surrounded by a cell -wall, and in each cell 

 we find a nucleus lying in the protoplasm, accompanied by one or more vacuoles. 



Fig. 46. Basidiobolus rauariitn. Fig. 47. Basidiobolus ranarum. After ElDAM. 



After Raciborski (1896). /.Grown /, Young branched plant (x 60). 7^; Young plant 



in 20 per cent, solution of glucose. with erect conidiophores. Co, Conidia (x 30). 



//, Cultivated in a 10 per cent, solu- ///, Early stage in the formation ofazy^ote (X 350). 



tion of sugar at a high temperature. IV, Formation of a zygote from two conidia (X a^o). 



///, Giant cell from a similar cul- V, Later stage of /F(x 250). 

 ture, without cell-walls but with 

 several nuclei. IV, Palmella stage 

 grown in a solution of glucosi; and 

 ammonium sulphate. 



The cell grows in the culture fluid, it becomes longer, and finally forms medianly 

 a transverse wall by which it becomes subdivided into two cells. Previously 

 division occurs in the nucleus, and each daughter-nucleus finds its way into one 

 of the ' daughter-cells'. The division is a concomitant of growth, and although 

 both cells remain united, each possesses an individual vitality, and exhibits 

 all the features of a Basidiobolus. The cells may be isolated and each 

 cell is then seen to be quite independent of the other, growing and dividing 

 on its own account. Growth then takes place not in one direction only, the 

 long axis, but lateral branches appear (Fig. 47, /) which, however, do not call 

 for further mention here. If the composition of the culture remains unaltered 

 growth and cell division proceed for an unlimited time in the same way. On 

 the other hand, remarkable changes in form may be induced by altering the 

 composition of the nutritive solution (Raciborski, 1896). If the concentration 

 be greatly increased and a 20 per cent, solution of sugar be supplied instead of 

 10 per cent., or if sodium chloride or another mineral be added up to 6 or 10 per 

 cent., growth in length is inhibited, the cells become more rounded, and the 



