THE WEB OF LIFE 299 



which seem to help to oil the wheels, so yeasts may also 

 be co-operative. An instance is given by Dr. Karel Sulc, 

 who found various yeasts of the Saccharomyces (ordinary 

 yeast) type Hving inside the accumulated reserve material 

 of Aphides, Scale-insects, Cochineal insects, and the Uke. 

 There is evidence that they are not passive inclusions, but 

 that they work out changes in the stores. 



In the interesting caterpillar of Nonagria typhce, which 

 feeds inside the stem of bulrushes, the digestive area is very 

 restricted, and Portier could find no evidence of a ferment 

 able to digest cellulose. But there were present in great 

 abundance very minute organisms, which he calls ' pseudo- 

 bacteria ', probably of the nature of moulds, which work 

 at the vegetable tissue and break it down. They pass 

 through the wall of the intestine and are engulfed by the 

 caterpillar's amoeboid blood corpuscles. The case is a 

 very extraordinary one and must be re-investigated, but 

 it looks Uke a genuine partnership, as if the ' pseudo- 

 bacteria ' were middle-men between the animal and its 

 food. We are reminded of the beautiful Infusorians which 

 seem to be always present in the horse's intestine, helping 

 in the breaking down of the hay and other foodstuffs. 



The microbe (Pseudomonas radicicola) of the root-nodules 

 of Leguminous plants occurs also in some members of 

 other orders. Prof. Bottomley has found it forming 

 nodules in the lateral roots of the bog-myrtle {Myrica 

 gale), and has shown that young plants, grown in steriUzed 

 soil poor in nitrogen, do not flourish unless they have the 

 root-nodules, and that root-nodules are produced on unin- 

 fected plants after they are treated with a culture of the 

 microbe. Miss Spratt has also found the same form in 

 an alder {Alnus incana) and in two buckthorns (Elwagnus 



