82 



THE FERN BULLETIN 



rapidly disappearing before the encroachments of 

 other vegetation. The species which has undoubtedly 

 been introduced is said to have been noticed first by 

 Dr. Barker of De Pauw University in 1904. 



Ferns as Weeds. — Although ferns grow in great 

 abundance in suitable spots throughout the world it is 

 seldom that they become weeds. In newly cleared 

 land in temperate regions the bracken may persist for 

 a few seasons, and compete with the cultivated plants 

 and nearer the equator other species may plague the 

 cultivator in the same way, but in such cases the plants 

 lack one of the essential qualities of weeds, namely, the 

 ability to multiply and spread into new regions. As a 

 general proposition ferns are not increasing in num- 

 bers anywhere. The nearest approach to this condi- 

 tion is seen in some of the fern allies. The field horse- 

 tail ( Eqidsetum arvense) is undoubtedly a weed and 

 quite able to spread into new territory, but with the 

 exception of its harmful presence in low meadows, it 

 may be questioned whether it is not more helpful than 

 the reverse in which case it cannot be called a weed. 

 Certainly a good many railway embankments are kept 

 from washing by the matted stems and rootstocks of 

 this species. And even in such places it seldom spreads 

 at the expense of other plants. It is only when there is 

 room that it takes an area to itself. The same is true 

 of the water clover (Marsilia) and the azolla. They 

 may fill up ponds where they gain a foothold but not 

 to the exclusion of other species. In the topics, also, 

 a few ferns may behave in the same way. Ptcris longi- 

 folia, and Adiantum capillus-veneris are fond of grow- 

 ing on old walls of every description and several others 

 may take up positions on the roofs of houses, but 



