PLATE XVI.— RUST OF WHEAT. 



(After Dodel-Port, Ik Bary, and Tulatne.) 



The Rust of Wheat is interesting on various grounds, for the varied forms it assumes, and the change of quarters it delights in, as 

 well as for the effects produced by it. It has a curious history, owing to the fact that its connection with the Barberry was recognised 

 by farmers in practice long before scientific men had traced or even dreamt of the connection. It was found out that in going its various 

 rounds in order to complete its life history, there existed the same relation between Rust and Barberry as between Lodger and Boarder. 

 Although so well investigated, no remedy has yet been found for its ravages. 



Fig. 1. Leaves of Barberry bearing yellow or orange patches on stalk and blade — the Aecidium-fruit. 

 Towards the end of summer these patches appear, called Barberry rust. 



Fig. 2. Transverse section of such a leaf. 



The mycelium of the fungus has penetrated through the tissue of the leaf, extracting nourishment and draining 

 the leaf by the way. It has also produced a fructification of two kinds ; one on the upper side, the other on the 

 under side of the leaf. 



The Spermogonia are flask-shaped bodies on the upper surface, producing numerous filaments called Spermatia. 



The Aecidium-fruit on the under surface is a globular body surrounded by a wall or peridium, which on open- 

 ing allows the spores to escape. 



Fig. 3. Aecidio-spore germinating. 



It sends out two filaments, which branch and form the Mycelium of the Rust. 



Fig. 4. Streaks of a rusty colour appear on the surface of the leaf owing to the Uredo-spores bursting through. 



Fig. 5. Transverse section of leaf. 



The mycelium ramifies through the tissues of the leaf; and towards the surface, branches produce the Uredo- 

 spores. These cause a swelling, and the epidermis ruptures, when the spores are easily blown about by the wind. 



Fig. 6. Uredo-spores produced late in the summer along with Teleuto-spores. The double coat of the Uredo-spore is relatively 

 thin, and covered with minute projections, while that of the Teleuto-spore is thick and brown. 



Fig. 7. Uredo-spore germinating, and giving rise to a branched mycelium in the leaf, which again reproduces Uredo-spores, and 

 so on. 



Fig. 8. Teleuto-spore germinating. 



This spore is two-celled, and was formerly supposed to belong to a different fungus, which was named Puccinia 

 graminis. 



It forms a branching pro-mycelium of several cells, from the branches of which Sporidia arise. 



Fig. 9. A Sporidium falling on the Barberry, when it is to be found in hedge-rows adjoining corn-fields, germinates on the under 

 surface of the leaf, and produces the form in Fig. i. 



Life History. — The Cluster-cups, or Aecidium-fruits on the Barberry, produce numerous Aecidio-spores, which germinate on the 

 damp leaves of Wheat There a mycelium is formed, the Uredo, which gives rise to Uredo-spores, forming the rusty powder 

 on the surface of the leaf. The Uredo-spores, or Summer-spores, may in turn germinate on a leaf of Wheat, produce a 

 mycelium giving rise to Spores, and this course may be repeated over and over again, spreading the Rust till the harvest 

 season. Then Teleuto-spores, or Winter-spores, are produced, which germinate next spring, and develope Sporidia at the end 

 of branches of a short .filament, which can form the Aecidium-fruits on the young Barberry leaf, as in Fig. i. 



The Rust of Wheat may appear even before the appearance of Barberry leaves, owing to the Uredo-spores persisting 

 during the winter and directly germinating on the young Wheat 



