34 Infection. 



and this was called Local infection. Then it was discovered that the young 

 ovary or other portions of the flower might be infected by the germ-tube of 

 the spore producing in some cases a mycelium inside the seed, so that when 

 the ripe seed was sown next season, the resulting plant was diseased. This 

 is known as Flower infection and occurs in Ustilago tritici and U. nuda. 



Next Hecke-i discovered a fourth mode of infection, which he called Shoot 

 infection, and it was suggested by what occurred among the numerous Lychnis 

 plants which had been grown from seed obtained from the flowers that had 

 been infected. Such seed produced nothing but sound flowers in the summer, 

 but one plant formed a smutted flowering shoot in October (autumn). There 

 were, at least, two possible explanations of this. It might be accounted for 

 by flower infection, the summer flowering shoots escaping by their rapid 

 growth, while the fungus reached the growing point of the more slowly de- 

 veloping autumn flowering shoot, or there was the possibility that the plant 

 was originally sound and was subsequently infected by neighbouring diseased 

 plants grown in pots alongside. Such an infection could only be conceived to 

 take place by the mass of spores falling to the ground, germinating there, and 

 producing their conidia, which reached and infected the young shoots 

 arising at the collar or top of the root. In order to prove this possibility, he 

 experimented with perfectly sound two-year old plants of Lychnis alba. They 

 were grown from seed in pots and cut back in October as far as possible to the 

 collar or the portion level with the ground. Then the exposed collar was dusted 

 with spores of Ustilago violacea and covered with manure containing similar 

 spores. A few weeks afterwards the freshly formed shoots appeared at the 

 surface, and in May of the following year began to flower. The flowera pro- 

 duced were smutted and their diseased condition can only be referred to the 

 shoot infection which took place in October. 



The Anther smut {Ustilago violacea (Pers.) Fckl.) is able to produce its 

 spores only in the anthers or male organs. This fungus infects the Campion 

 {Lychnis dioica) which has the sexes on separate individuals, and it not only 

 attacks the male plant where the anthers are normally developed but also 

 the female plant which normally never bears them. In the male plant it 

 produces its violet spores in the anthers naturally present, but in the female 

 plant it still produces its spores, although anthers are absent in the natural 

 conditio]!. It stimulates the female host in some way to the production of 

 stamens in which it may develop its spores, while the pistil normally 

 developed, is suppressed. The fungus is evidently able to induce the con- 

 ditions necessary to the formation of male organs, although elaborate experi- 

 ments by Strasburger failed to produce this effect in uninfected plants. 

 We must assume that both sexes exist, but the dominant one only becomes 

 visible while the other remains latent, and this dominance may be controlled 

 by an internal stimulus which may influence the particular kind of nutriment 

 available. Change of sex is here shown to be possible, but how it is brought 

 about cannot be definitely stated, further than that it is determined by 

 internal, not external factors, and since it is the young shoots which are 

 infected, the sex may be determined long before the appearance of the 

 flower. 



A similar experiment was made with Urocystis occulta. The perennial 

 Secale montanum was employed as a host-plant, after it had been shown that 

 plants of this species, which were cultivated in gardens, became naturally 

 infected by Urocystis occulta produced upon the rye {Secale cereale). In this 

 experiment all shoots were likewise cut back to the collar and then infection 

 was made in the autumn with spores and manure containing spores. The 

 result was that in the spring of the following year, the shoots produced were 

 smutted. 



