[Crown Copyright Reserved, 



ROYAL BOTANIC GARDENS, KEW. 



BULLETIN 



OF 



MISCELLANEOUS INFORMATION. 



No. 



[1914 



XXII.— ON THE PRESENCE OF HYBERNATING 



MYCELIUM OF MACROSPORIUM SOLANI 



IN TOMATO SEED. 



I, Massee. 



(^VITII PLATE.) 



It lias iowg been suspected by tomato growers that tlie germ of 

 'Vblack-rot '' of tomatoes, Macrosporiavi solani, Cke., was 

 carried in the seed, but, so far as I am aware, tlie actual presence 

 of my-celium in the seed has not been previously demonstrated. 

 When tomatoes are attacked by '^ black-rot/' the seeds often show 

 black spots on the surface. Massee* proved that when such seed 

 Avas sown, either no germination took place, or else the resulting 

 plants often showed ** stripe'^ disease. Microtome sections of 

 such spotted seed proved the presence of mycelium in varying 

 quantities. In a healthy tomato seed the testa is in close con- 

 tact with the endosperm, but in an infected seed a thick weft of 

 closely compacted hyphae is present between the t^st^ and the 

 endosperm. When a tomato is badly infected with *^ black-rot" 

 the mycelium extends deeply beneath the diseased patch, and in 

 many cases the placentas are completely permeated with a dense 

 weft of mycelium, which causes them to become quite black. As 

 would be expected, the seeds borne on these blackened placentas 

 are also often attacked by the mycelium, which enters through 

 the micropyle. The weft of mycelium is sometimes of uniform 

 thickness all round the endosperm, in other instances the thick- 

 Uess of the w^eft varies at different points, and sometimes it is 

 confined to one or two isolated patches. The hyphae are colour- 

 less, septate, and of variable thickness, averaging 4—5 fx. From 

 this peripheral weft of mycelium hyphae pass into the endosperm 

 and also into the embryo. These hyphae are both inter and 



* Massee, G. Journ. Board Agric, voL VS, p. 232 (1906). 



(3237.) Wt. 225-505. 1,125. 5/14. J.T.&S. G. 14. 



