195 



established itself in the interior of the stem, and if one sporo- 

 phore is removed another as a rule soon takes its place. 



Diseased trees must be removed as quickly as pos- Preventive 

 sible. Wounding and injuring living trees must be avoided, and Measures. 

 cut surfaces should be covered with tar or other protective sub- 

 stance. So far as we can, we must help the cambium to 

 cover over as quickly as possible all wounds which may arise. 



171. It has been estimated (4) Pyccmia 



that the annual financial loss in India, on account of fhegraminis 

 damage done to cereal crops by the fungoid diseases popularly ^ ers> . 

 known as Rusts, is probably not less than Us. 4,00,00,000. attacked. 

 The best known rust in India is Puccinia graminis which is 

 very destructive to wheat, and which we may also take as a 

 type of the great group of parasitic fungi to which the rusts 

 belong, viz. the Uredinaceae. 



The first sign of the disease consists in the appearance of Signs of the 

 orange-red streaks and patches on the green wheat leaves, Dlsease - 

 culms and even on the ears, which in Northern India usually 

 happens in January February. These rust pustules swell 

 and, bursting through the epidermal tissue of the wheat 

 plant, scatter spores which look like reddish dust and are 

 called uredospores. 



If the tissues of the wheat plant are examined with Life History 

 the microscope the mycelial threads of the fungus will be and Damage 

 found ramifying in all directions between its cells. This done> 

 mycelium derives its nourishment from the green cells 

 of the wheat plant and consumes the food materials 

 which should go to form the grain ; consequently the yield 

 of the latter is enormously reduced. After growing and 

 spreading in the tissues of the wheat plant for two or three weeks 

 the hyphse turn towards the epidermis, and the orange, oval, 

 one-celled uredospores are budded off from their tips ; the 

 gradual accumulation of these hyphal branches and the spores 

 which they shed result in the swelling of the pustule and 

 ultimate rupture of the epidermis with the scattering of the 

 spores. If these spores fall into water they germinate and 

 send out two or more germ filaments [see Plate XIX (2)], one of 

 which outstrips the rest and either dies in the absence of a 

 suitable host or, in the event of its having alighted on a wheat 

 plant in a drop of rain or dew (which would often happen in 

 a wheat field), finds its way into a stoma and rapidly gives 

 rise to a new mycelium, which in due course produces a fresh 

 crop of uredospores. The function of these spores is thus 

 to spread the disease rapidly from plant to plant, wind aiding 



