34 



Letters on the Diseases of Plants. 



o£ view. The uredospores of the disease (the teleutospores are rare on 

 peach-trees in this Colony) can be made to germinate very readily in water in 

 a moist chamber. When so germinating their usual 

 appearance is shown in Figs. 39 and 41. On one 

 occasion, however, I observed an apparent amalga- 

 mation of the promycelium of three adjacent spores. 



Fig. 44.— Conidia that arise 

 from the miuute black 

 pycuidia shown as grow- 

 ing in the rust-pxistules of 

 peach in Fig. 40. The 

 upper spore is shown as 

 it issued from the pyc- 

 uidium, the next lower 

 has begun to germinate. 

 The next two show 

 further stages of the ger- 

 mination, which takes 

 place somewhat after the 

 manner of the growth of 

 the yeast plant. The lower 

 figure,however, shows one 

 of these same spores pro- 

 ducing a S, well-developed 

 mycelium. 



Fig. 43. — Three 

 uredospores of 

 the peach-rust 

 fungus, whose 

 mycelia, germi- 

 nating in water, 

 have amalga- 

 mated. 



The appearances are faithfully shown in Fig. 43. 



The only doubt that can possibly arise is that the 



hyphse became entwined and thus deceived me, but I hardly think this 



can have been the case. Again, I frequently find among the uredospores of 



l^ycnidium growing among the viredo- 

 of acacia. One of the two-celled conidia 



Pig. 45.— Small black 

 spores of the rust of 



arising from this pycnidium is shown above more highly 

 magniiied. This rust may be described as follows : — 

 Mclampsoi-a 'phyllodionmi, B. and Br. livedo stage. — The 

 roimd uredo sori,' which are only two to three-tenths of a 

 miUimetre in diameter, occur on both surfaces of the leaves 

 of the host-plant, and are usually crowded together in 

 large numbers, and then cause wart-like growths of a dark 

 brown colom-. The thickening of the leaf under the sori is 

 dxie to mcrease in the tissvaes. The yellowish brown obovate- 

 elongate lu-edospores are borne on i^edicels nearly twice 

 as long as themselves, and are unaccompanied by paraphyses. 

 The spore-wall is moderately thick, and its surface is marked 

 with short obtuse echinulae or warts, arranged in longitudinal 

 and transverse rows like the grains on a cob of maize. The in- 

 ternal cavity, especially of the transparent yoiuig spores, which 

 are as usual larger in proportion to the vndth than mature 

 spores, is somewhat cyhndrical — that is, is truncate at the ends, 

 especially so at the apex. The mycelium averages only 2 M- 

 in diameter. Each matiu-e spore is possessed of fovir equatorial 

 germpores, and has, on the average, the dimensions 17 x 41 M. 



As the uredospores fall away a pycnidium appears in their 

 place, apparently from the same mycelium that produced the 

 uredospores, at all events in the centre of the same sorus. These 

 pycnidia are nearly spherical, and have a small ostiole 

 aroimd which the peridium is nearly black. We have seen 

 this growth repeatedly, and have exammed it closely by means 

 of very carefully made sections, and believe it to be normal. 

 The connection with the uredospore sorus is so intimate that 

 it is diiiicult to form any other opinion than that the m-edo- 

 spores and perithecia originate from the same mycelium. 

 Puccinia stage. — I have not seen the teleutospores. 



Fig.46.-Sporefromthepns. ^ pustulc of this rust Small black pycuidia produc- 



tuie shown on Fig. 45, very ing a multitude of two-cellcd sporcs, which, when 



much more enlarged. ^^^^^^ .^ ^ ^^.^^ chamber, often bud and multiply 



after the manner of yeast plants, but which occasionally produce a mycelium. 



Further, I find in the pustules of a number of Australian rusts similar 



tiny black pycnidia, producing similar two-celled spores which behave in 



