146 



intra-cellular, of about the same thickness as the peripheral 



mycelium, sometimes closely septate, sometimes sparinglj- so. 



The hyphae probably dissolve the very thin walls of the cells by 



i^neans of a ferment, as described by Marshall Ward in his account 



'of the perforation of the cell walls by the Botrytis in a '^ Lily 



Disease/'t When the tip of a hypha comes in contact with a 



^ell-wall it becomes flattened and rather swollen, and a thin portion 



from the centre of the flattened part in contact with the cell pierces 



Uie wall, and swells up at the opposite side to the normal thickness 



of the hypha. In other instances the hyphae appear to pass 



through the wall without any preparatory flattening and swelling. 



No haustoria are present 



On the germination of infected seed, one of two things may 

 happen; either the embryo is killed almost at once by the my- 

 celium, when present in considerable quantity, or the mycelium 

 grows along with the seedling, in whose tissues hyphae can be 

 distinctly traced. In such infected seedlings the ^^stripe '^ form 

 of the disease has been produced before the plants were two 

 months old, when grown under favourable conditions for the 

 rapid development of the fungus, namely, an excess of heat and 

 moisture. Sections of diseased seed which had been kept dry fox 

 some months, when placed on damp filter-paper in a Petri-dish, 

 were soon surrounded by a copious development of hyphae, show- 

 ing that the mycelium present in the seed retains its vitality for 

 a considerable period of time. 



In many instances, when the seed produced by a diseased 

 tomato does not contain mycelium in its substance, it is sur- 

 rounded by a weft of hyphae which cannot be removed in the 

 ordinary process of cleaning, being held in position by the dense 

 coat of hairs covering the testa. This external mycelium is also 

 a source of danger, and the only certain means of avoiding 

 disease due to infected seed is to reject all seed produced by 

 diseased fruit, even if it does not show the black spots. 



EsPLAXAXroX OF THE PlATE. 



Fig. 1. — Section of portion of a sound tomato seed, showing parts of the 



coiled embryo (a) and endosperm (&) ; x 75. 



,, 2. — Diseased seeds of tomato, showing black patches on the 



testa ; x 3, 



„ 3, — Section of portion of a diseased tomato seed. The mycelium is 



coloured red. 



,, 4. — Section of portion of a tomato seed showing a weft of mycelium 



situated between the testa and the endosperm, hyphae from 

 this weft are seen passing into the tissue of the endosperm. 

 Mycelium coloured red. x 400. 



j> 5, — A similar section of fig. 4, showing the mycelium permeating the 



endosperm. Mycelium coloured red. ^ x 400. 



„ 6. — A strand of mycelium entering into the embryo (a) from the 



endosperm, {h) mycelium coloured red. x 400. 



„ 7 and 8. — Methods by which the hyphae pass through the cell-walL 



Mycelium coloured red. x 400. 



t Ann. Bot., 2, p. 319 (188D) 



