140 



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



experiments to see whether starving the host-plant of one or other 

 of its necessary food-materials would (1) affect its predisposition to 

 infection, or (2) affect the capacity for infection of the fungus grown 

 on the starved plants, or (3) in any other way affect the fungus or its 

 host. 



On July 7, 1902, fourteen beakers were selected and filled with 

 equal quantities of a clean coarse-grey sand, carefully washed and dried, 

 but still containing traces of ingredients which the root-hairs of such 

 grasses as the Bromes are capable of selecting. This was not to be 

 avoided or regretted, since my object was not to attempt to grow seed- 

 lings totally deprived of necessary salts, resulting in their premature 

 death, but to bring up plants so starved of certain such ingredients 

 that while they could go on living long enough for the purposes of 

 the experiment, they would nevertheless exhibit the effects of the 

 deficiency, and possibly re-act on the parasite. 



The beakers of sand were lettered A to 0, and treated as follows : — 

 The beaker A received 200 c.c. of distilled water only, so that the 

 only mineral supplies available to the seedlings — after exhausting the 

 traces in the endosperm — would be such as the root-hairs could dis- 

 solve from the sand grains. Another beaker received an equal 

 quantity of a cold water-extract of fresh horse-dung, representing a 

 liquid of high manurial value. A third beaker received an equal 

 quantity of a normal nutritive mineral solution containing nitrates, 

 phosphates, and sulphates of potassium, calcium and magnesium ; and 

 a fourth the same with the addition of five drops of a dilute solution 

 of ferric chloric. 



One each of the remaining beakers received a similar solution of the 

 nutritive salts, but in each case with the omission of one element, 

 viz. : calcium, magnesium, nitrogen, phosphorous, or potassium ; while 

 the other beaker of each pair received the same, together with traces 

 of iron salt. 



By these means I had prepared a soil in each beaker which was of 

 suitable consistency for growing such sand-loving grasses as Bromes, 

 but which was in each case deficient in one or other of the necessary 

 ingredients for normal nutrition— except in so far as I added such in- 

 gredients — but in no case absolutely devoid of these necessary salts, 

 as otherwise the seedlings could not be expected to live long enough 

 for the purposes of the experiment. 



On July 8. having allowed the solutions to soak completely into* 

 the sand, seven grains of Bromus secalinus, carefully cleaned and 

 selected, were sown in each beaker, and the whole left under large 

 bell- jars to germinate in a suitably lighted position in the laboratory. 

 Germination followed in due course, though somewhat slowly, as the 

 sand was rather wet, and on July 15, from two to five seedlings about 

 30 — 50 mm. high were showing above ground in each beaker except 



