Prof. H. Marshall Ward. Effect of Mineral [Nov. 4, 



It now remained to test the further ques- 

 tion : — Are such spores equally capable of 

 infecting other seedlings 1 



In order to test the capacity for infection, 

 or virulence, of the spores developed on the 

 experimental plants, I employed tube-cul- 

 ; tures of seedlings as described in a previous 

 in communication,* with a slight modification 

 I in detail, as follows (see fig. 4) : — 

 > Picked grains of Bromns secalinus were 

 ] sown singly in test-tubes of sand, to which 

 ) the normal mineral solution was added, and 

 s sterilised. When the seedlings were well up, 

 f and nine days old, on August 14, each having 

 I one good green leaf, a sowing was made on 

 5 each from the uredo pustules on one of the 

 5 plants of Experiment 47 (Table I), as shown 

 = in the annexed tabular summary (p. 147). 



It will be seen that in every case the 

 i results of infection were positive. Those 

 J spores which had been reared on seedlings 

 § starved of phosphorus (/?), and on those 



starved of all salts (a), were behind the 

 \ others in their rapidity of effect; but we 



1 cannot lay much stress on this, because the 

 f same was true of spores reared on what 

 I should have been the calcium-starved plants 

 ? (c), which accidentally received a dose of 

 | calcium by mistake. On the other hand, the 

 q most vigorous spores were those reared on 

 3 plants to which horse-dung decoction had 

 | been added. 



1 I am. not disposed to lay stress on these 

 3 latter points, however, but am content at 

 =j present to regard the positive results as 

 [ amounting to proof that spores even when 

 K reared on starved seedlings are capable of normal 

 ^ germination and infection when placed on the 

 leaves of other — normal — seedlings. 



A second experimental series of sand- 

 cultures was started on July 10, 1902, in 

 sixteen beakers, arranged as before, but with 

 the following differences in detail. The sand 

 used was a -finer and whiter silver sand, 

 # " On Pure Cultures of a Uredine.' 3 'Proc. Eoy. Soc./ vol. 59, p. 451. 



