TRANSACTIONS OF SECTION K. 837 



ID tubes, but uot infected, gave rise to no uredo, even if raised from the seeds of 

 diseased plants. The pustules of uredo only originate at that spot on the leaves 

 where the uredo-spores were sown. 



These results lend do support, therefore, to any hypothesis of internal or 

 seminal infection. 



Long series of sowings were made to test the conditions of germination of 

 the uredo-spores, for, strange as it may seem, little attention has been paid to this 

 matter. The minima aud maxima temperatures of germination are about 10° C. and 

 '27°-5C. respectively, the optimum being about 18° C Many failures in infections 

 are due to the non-germination of the spores in hot weather. 



The ertects of light, of other organisms {e.r/., Algte), of various extracts, and of 

 the age of spores, &c., were also examined. 



The uredo-spores may be frozen for ten minutes, but will not recover after two 

 hours' freezing. 



Infection experiments on pot plants were made — several hundreds in all — 

 on twenty-one species or varieties of Bromus. 



The general results are, put very shortly, as follows : Although the uredo 

 examined is in all morphological respects absolutely identical on all the species of 

 Bromus on which it occurs, nevertheless if spores gathered from B. sterills are 

 sown on B. mollis the infection fails, whereas spores of the same batch sown on 

 B. sterilis infect normally and rapidly. And similarly in other cases. Spores from 

 B. mollis readily infect B. mollis, and (less certainly) its allies B. secalinus and 

 B. velutinus, B. arvensis and others of the Serrafalcus group; but they fail on B. 

 maximus, B. tectorum, B. sterilis, B. 7>iadritensis,&c.—tha Stenohromus group — aud 

 so with other cases. 



[Tablks I. and II.] 



In the annexed tables (I. and II.; are tabulated the results obtained in seven 

 of the experimental series. The tables explain them.selves, but it may be well to 

 note that the species of Bromus employed as host-plants have here been arranged 

 in similar order throughout in order to facilitate comparison. Thus B. erectus to 

 Ji. ciliatus are representatives of the first group {Festucoides) ; B. fectorum to 

 B. maximus, inclusive, of the second group {Stenohromus) ; B. secalinus to B. 

 macrostachjis, inclusive, of the third group (Serrafalcus) \ and B. unioloides, with 

 which B. Schraderi is synonymous, of the fifth group (Ceiatochloa), The author 

 has uot yet had time to examine B. arduennensis (fourth group), and in a few 

 CAsesthe series of experiments are too few for any statements of value as to details. 

 But it seems clear that the general statement is sutiiciently proved as regards 

 groups 2 and 3 at least. 



The series selected for tabulation in the foregoing tables are only a few taken 

 from the numerous sets of similar experiments. This is hardly the place for 

 reproduction of many other details, but in order to give some idea of the enormous 

 amount of labour involved in such an investigation, another table (III.) is appended 

 giving a summary of all the series of this season's pot-plants under normal condi- 

 tions only, exclusive of experiments with tubes and with extraordinary conditions 

 such as diminished mineral supplies, and so forth. 



Here, again, it will be seen that the general accuracy of the conclusions put 

 forth is fully evident, though a detailed examination of 'the series — conditions of 

 infection, incubation, &c. — is necessary for the explanation of one or two apparent 

 discrepancies — e.r;., to explain why the percentage of failures was so high with B. 

 w/M^iViK;: infected with spores from B. secalinus. These matters must be left for 

 future treatment, and in some cases for further experiments next season. 



[Table III.] 



Thus, in the annexed Table III. we see that eighty-five plants of B. mollis were 



inoculated with uredo-spores derived from B. ^zoHis, of which sixty (over 70 per 



Cent.) gave positive results, i.e., actually developed pustules at the spots inoculnted ; 



but it should be noted that in many cases bare" recorded as failures — because I put 



1901. ' 3 I 



