xvi STORY OF RUST IN WHEAT 191 



therefore means that the plant has less power of 

 starch-making, and therefore the grains are small 

 and light. 



That the cause of these streaks was a fungus 

 was known some centuries ago, and as soon as the 

 development of the microscope permitted, it was 

 recognised that the powder on the infected plants 

 was what the older botanists called the " seeds " of 

 the fungus, and what the modern ones call spores. 

 That by these spores fresh plants could be infected 

 was an obvious conclusion, which was drawn com- 

 paratively early. For instance, Sir Joseph Banks, 

 writing in 1805 for English farmers, gives the 

 following account of what was then known as the 

 fungus. He does not, we must remember, profess 

 to put forward anything new about the fungus, but 

 simply to tell farmers what the botanists thought 

 at this time. 



He begins by explaining that on the surface of 

 the leaves and stems of the grasses there are minute 

 pores. He regards these pores as a means of taking 

 in water, for he says : " A plant cannot when 

 thirsty go to the brook and drink, but it can open 

 innumerable orifices for the reception of every degree 

 of moisture, which either falls in the shape of rain 

 and dew, or is separated from the mass of water 

 always held in solution by the atmosphere ; it 

 seldom happens in the driest season that the night 



