1902.] Starvation on the Parasitism of Puccinia. 149 



Control cultures have shown over and over again that these seedlings 

 do not incur the disease unless the spores are placed on the leaves, 

 and I cannot accept these one or two apparent exceptions as evidence 

 for a spontaneous outbreak of the disease. 



The severity of the attack, as indicated by the size of the pustules 

 and of the infected areas, and by the relative number of spores 

 developed, followed much the same order as in the previous experi- 

 ment, except that the nitrogen-free plants seemed to bear larger 

 pustules than before. 



The minute and poorly-developed pustules on the seedlings starved 

 of phosphorus (I and m, Table III) or of all minerals (a) were par- 

 ticularly evident; as also were the severe attacks of the manured 

 specimens. And, again, the magnesium-free seedlings showed pre- 

 mature yellowing and withering of the leaf -tips. Again, also, there 

 was decided retardation of infection pustules in the phosphorus-free, 

 distilled water, and, to a less extent the magnesium-free specimens. 



But — again concordant — none of the plants were rendered immune 

 from infection ; and, as will be seen in the sequel, all the pustules, 

 however minute, yielded spores with normal morphological characters, 

 and perfectly capable of germinating and of reinfecting other seedlings 

 of the Bromus in question. 



Meanwhile, I had started a third complete series of sand-cultures of 

 Bromus pendulinus, arranged as in the last series, but with two small 

 variations in detail, viz., (1) in order to diminsh the risk of drowning 

 or asphyxiating the seeds, I sunk a tall thistle-head funnel to the 

 bottom of each beaker of sand, and poured the solution in each case 

 down to the bottom of the beaker, allowing it to soak upwards and 

 gradually moisten the upper laj^ers from beneath; and (2) only 

 5 grains of the Brome (B. pendulinus) were sown in each beaker. 



The results were very good. The grains were sown July 23. On 

 July 29 seedlings were up in all but three of the beakers. On August 1 

 these also had seedlings showing, and by August 5 most of the seed- 

 lings were 25 — 30 mm. or more high. 



On August 9 all but three of the beakers had four or five excellent 

 seedlings, each with the second leaves showing, and the effects of the 

 mineral starvation were beginning to be visible. 



In order to emphasise this effect, if possible, by preventing the 

 further development of the second and later leaves at the expense of 

 materials stored in the first leaves, I now cut off the latter from each 

 seedling with a pair of sharp fine scissors, and left the seedlings to 

 grow further. During the next week the second leaf in each case 

 attained its full size, and the third leaf began to appear ; and I now 

 proceeded to devote this series of seedlings to test the effect of sowing 

 the spores reared on the seedlings of the last series (see Table III), and 

 which had been affected as to their numbers by the starving or other 



