568 DISEASES OF CULTIVATED PLANTS 



dark brown or olive-green blotches on the leaves, varying 

 from one to four mm. diameter. 



Hyphae springing in dense, crowded tufts, brown, often 

 more or less crooked, sparingly septate ; conidia usually 

 narrowly clavate, pale brown, 1-3 septate, 35-55x6-7 p. 



Lilac leaf blotch (Heterosporium syringae, Oudemans) 

 forms large, irregularly shaped, greyish-brown, dry blotches 

 on lilac leaves. The fruit of the fungus forms small blackish 

 tufts which emerge through the stomata, or burst directly 

 through the epidermis. 



Pustules, black, regularly distributed on the patches, 

 conidiophores septate, irregularly flexuous, slender, conidia 

 very pale olive, 1-3 septate, wall minutely warted, the largest 

 cylindrical, ends rounded, 25-30x7-9 p. 



Klebahn, H., Krankheiten des Flieders, p. n (1909). 



' Internal disease ' of potato tubers. This disease up to 

 the present has not been thoroughly understood. The 

 general symptoms are the presence of more or less scattered, 

 small rusty spots in the flesh, which is usually watery in 

 an advanced stage of disease. Externally the tubers show 

 no symptom of discoloration or disease. Sometimes ex- 

 amples of tubers said to show * internal disease ' have proved 

 to be incipient cases of winter rot, caused by Nectria solani. 

 In other instances, however, no trace of mycelium can be 

 found in the diseased areas. 



Quite recently Home has paid attention to this disease, 

 and in a preliminary note announces the presence of an 

 endophyte, which has been found to be constantly present 

 in all tubers affected with ' internal disease ' that have been 

 examined. The author states : 'Although the organism may 

 exist within the cells of the host without doing any visible 

 damage, it is capable under certain circumstances of causing 

 deterioration and death of the host cells.' 



The organism is said to begin growth as a small vesicle 

 within a cell, being attached by a fine thread to the wall. 

 These vesicles increase in size and form bladdery, sphaer- 

 oidal, or lobed bodies in cells with scanty contents. In cells 

 containing starch the organism is flattened between the starch 

 grains. The vegetative body gives rise to one or more 

 spheres, capable of producing by budding at a number of 

 points, a sorus of sori or sporangia within the membrane of 



