Letters on the Diseases of Plants. 35 



precisely the same manner. Among other rusts producing these bodies is 

 that occuring on acacias, and that which occurs on a species of Agroptjron, 

 probably the species scahrum. There are, a priori, two ways of accounting 

 for these pycnidia: either — 1, they are parasites on the rust; or, 2, they 

 are an integral part of the rust, and represent another spore-form of the 

 rust. 



This is such an interesting subject that I have often wished to inquire 

 into it carefully but have not done so, solely for lack of time. Perhaps 

 someone more fortunately situated will undertake the task. These two- 

 celled bodies have, as I have on several occasions pubhcly remarked, no slight 

 resemblance to the so-called spermogonia of several species of Aecidium, and 

 this idea has already been fruitful of considerable discussion. Do not the 

 various bodies that 'have in this connection been called spermogonia and 

 spermatia need a more cai'eful examination than they have yet received ? 



As I before remarked, the teleutospores of the stone-fruit rust (or rusts) 

 are not common on peach-leaves in Australia. I have noticed that when 



peach-trees grow in close juxtaposition to 

 plum-trees the teleutospores are not un- 

 common on the peach-leaves as well as on 

 those of the plum. This certainly suggests 

 that there are either two species of rust 

 occurrino- on the peach or that there are 

 at least two distinct forms, whether or not 

 they be regarded as distinct species. This 

 observation is entirely in accord with the 

 conclusions of a number 

 of observers who have 

 during recent years 

 given close attention to 

 the forms and physio- 

 logical characters of a 

 number of other common 

 rusts. The form of the 

 teleutospores growing 

 on plum leaves is shown 

 in I'ig. 42. 



4. Shot-hole. 



This disease is one 



that is very common on 



the apricot, both on the 



leaves and on the fruit, 



some observers to the 



contrary on this latter 



point notwithstanding. 



In Australia, at least, whenever 



^tct'e^bf^L willZ^:^- Jlf :i the leaves of apricot-trees are 



shot-hole hmgus. Z"'' ![ badly riddled by this disease, the 



fruit rarely escapes inj ury . One 

 side of the fruit becomes scabby 

 from the attacks of the same fungus that attacks the leaves ; and often 

 when the fruit is attacked in a young stage it is ruined, as it fails to grow 

 on one side, and does not make much progress on the other. As to 



