1902.] 



Starvation on the Parasitism of Puccinia. 



145 



were apt to show early yellowing and withering, as well as some 

 degree of stunting. 



When we come to examine the results of infection, it is clear that 

 no great differences were observable between the various seedlings. 

 The first flecks — i.e., pale patches indicating the presence of the fungus 

 in the tissues — were visible on July 31 and August 1, that is to say, on 

 the eighth or ninth day after infection, and by August 3 pustules 

 were developed on all the plants except those starved of phosphorus, 

 while two days later even these were definitely pustuled in one of the 

 two beakers (h, Table I), though the other remained free of them to 

 the end (b, Table I). As will be seen from further experiments, how- 

 ever, we can lay no stress on this latter case, and must conclude 

 that : — Lack of minerals in no way secured immunity from infection, though 

 seedlings deficient in phosphorus or in nitrogen tended to show retardation of 

 infection. 



When we look into the matter from another point of view, however, 

 the conclusion seems inevitable that there are considerable differences 

 in the quantity of fungus mycelium, and consequently of Uredo-spores, 

 developed from the latter, which the various seedlings were able to 

 support. 



Taking the extreme cases, and comparing the sizes of the infected 

 areas on the phosphorus-free plants (h, Table I) and those on the plants 

 supplied with normal mineral solution (g and n, Table I), the latter 

 were found to be much the larger, and similarly with the pustules 

 themselves : the numerous large well-developed pustules on g and n 

 bore many hundred times as many spores as did the few small pustules 

 on /, and similar results were observable in less marked degrees on 

 others. It must therefore be concluded that : — Mineral starvation 

 makes itself felt quantitatively in the number of uredospores which can be 

 produced by the fungus in the tissues of the starved leaves. 



Now arose an important question : — Are the spores on the small 

 starved pustules in any way different from those produced by the 

 large well-developed pustules of normal or richly-manured plants 1 

 For instance, can any differences in size, colour, or marking, or in 

 capacity for germination, be detected in spores from the small and few 

 pustules of a, e, h, or I (Table I), and those from the large well- 

 developed pustules of g, n, or o ? 



As regards the morphological features, direct examination showed 

 that no differences were to be detected ; the properly ripened spores 

 in all cases were normal. 



As regards their capacity for germination, I proved by sowing them 

 in separate watch-glasses of distilled water that in every case the pus- 

 tules yielded spores capable of normal germination, and that in proportions 

 which showed no relation to the degree or kind of starvation of the seedling 

 which bore them (see Table II, col. 4). 



VOL. LXXI. M 



