hidigciioiis and Introduced Species. 63 



CHAPTEK X. 



Indigenous and Introduced Species. 



It is not always easy to determine what parasites are native and which 

 have been introduced, because although the introduced plant is liable to carry 

 with it the spores of some of the fungi which infest it in its native country on 

 the seed, or it may be only the hibernating mycelium inside the seed, yet 

 this is not invariably the case. While the potato has introduced into New 

 Zealand and Australia the well-known potato disease PhytophtJiora injestans, 

 the orange and the lemon in New South Wales are badly affected with a 

 disease caused by Phoma citricarpa, a fungus which is unknown elsewhere, 

 either in Italy or California, and wdiich has probably been derived from the 

 native Citrus trees. It will be safe, however, unless we have evidence to the 

 contrary, to regard as introduced those parasites which are found on intro- 

 duced plants. 



The term alien is usually applied to those species wdiich, although now 

 growing spontaneously, have been introduced through human agency. Such 

 alien plants are, therefore, often called introduced plants, although we may 

 have no definite information as to how they were brought here. In the case 

 of cultivated plants, such as cereals and some grasses, there is historic evi- 

 dence as to their introduction, but beyond that there is very little certainty. 

 A species, therefore, which is found wild amid natural sm'roundings may be 

 regarded as indigenous, Avhile those found amid artificial surroundings or as 

 escapes from cultivation, may be considered introduced. 



The introduced plants with smuts are confined almost exclusively to the 

 cereals, such as wheat and oats, barley and maize, and to a few grasses such 

 as rye-grass and Poa. From the principles laid down, the following may be 

 regarded as having been introduced : — 



1. Ustilago avencs (Pers.) Jens., on Avena saliva, or Oats. 



2. U. hordei (Pers.) Kell. and Sw., on Hordeum vulgare, or Barley. 



3. U. nuda (Jens.) Kell. and Sw., on Hordeum vulgare. 

 •i. U. tritici (Pers.) Jens., on Triticum vulgare, or Wheat. 



5. Cintractia sorghi-vulgaris (Tul.) Clint., on Andropogon sorghum.. 



6. Sorosporium reilianum (Kuehn) McAlp., on Zea Mays, or Maize. 



7. Tilletia levis (Kuehn), on Triticum vulgare. 



8. T. tritici (Bjerk.) Wint., on Triticum vulgare. 



9. T. striaeformis (Westd.) Oud., on Lolium perenne, and Poa annua. 



10. Urocystis tritici, Koern., on Triticum vulgare. 



There is no difficulty in accounting for the introduction of the above smuts 

 as the spores would be associated with the seeds, or the hiliernating mycelium 

 would be inside the seed, as in the case of loose smut of wheat and barley, 

 and both spores and mycelium retain their vitality sufficiently long to allow 

 them to be transported long distances. 



The only case calling for special remark is that of flag smut on wheat. It 

 is generally assumed to be the same species as that found on Rye in the Old 

 World, but since the spores from wheat will not infect rye, nor the spores from 

 rye infect wheat, it must be biologically distinct, and as a biological species 

 it may be called Urocystis tritici, Koern. The same form has also been found 

 on wheat in India and Japan, but how this biological species originated it is 

 impossible to say. 



