VII] PLANT POPULATION 107 



The Ferns also afford striking examples of an 

 extreme power of productivity. I have estimated 

 the number of spores of the Common Shield-Fern 

 {Nephrodium filix-mas) produced by a well-grown 

 plant in a single season at approximately 50 to 100 

 millions. But this is by no means the limit for plants 

 of that affinity, as the subjoined table shows, in which 

 the numbers quoted are estimated not for the whole 

 plant, but for the single leaf : 



A tliyrium filtx-foemina 1 6,000,000. 



Polypodium aiireum 96,000,000. 



Cyathea dealhata 200,000,000. 



Danaea 150,000,000. 



Ka nlfussia 1 73,000,000. 



Marattia 2,800,000,000. 



Angiopterls 4,000,000,000. 



The productivity of Fungi is well known, and 

 any one who has blown the spores off a fully matured 

 culture of some common Mould, and seen the dense 

 cloud that spreads into the air, would be prepared 

 for high numbers on a rough estimate being made of 

 them. In the common olive-green Mould {Aspergillus 

 herhariorum), the number of conidia produced upon 

 a single conidiophore or head is at a moderate estimate 

 about 1500. These heads are formed in countless 

 luimbers in a few days upon a suitable nutritive 

 medium. If 1000 of them were borne upon a single 



