856 REPORT— 1897. 



Two methods were pursued. In one each plant of the cereal was enclosed 

 from the beginning in a long glass tuhe, stufiied with cotton-wool above and below, 

 and so carefully protected against infection from wind-blown spores that we may 

 accept forthwith the improbability of such infection. 



Notwithstanding these precautions, the cereal was rusted at the same time as 

 its unprotected neighbours, and equally badly. 



Granting the accuracy of the experiments, only two explanations seem to 

 suggest themselves. Either (1) winter-spores attached to the grain had germinated 

 and infected the young seedling — a not impossible event, since several observers 

 have found spore-bearing mycelia in the pericarp of the ripe grains, and we know 

 these spores can conserve their germinating power for months ; or (2) the infective 

 material had been handed down to the embryo from the parent plant — an almost 

 inconceivable hypothesis. 



To answer this question Eriksson protected his seed-plants from external 

 infection, and sowed the grains in sterilised soil in specially constructed green- 

 houses, through which the air can only pass via cotton- wool filters. Between the 

 -double-glass windows water was allowed to stream, and the plants thus kept cool. 

 Some of these protected plants became rusted. 



Before we draw any conclusions from such difficult experiments as the above, 

 let us see the results of microscopic examination. 



Reference has already been made to the mycelium and spores in the tissues of 

 the pericarp of the grain ; no trace could be, or ever has been, detected in the 

 endosperm or embryo. In some cases the seedlings, four to eight weeks old, 

 •showed the first uredo-pustules on their leaves, and the mycelium but no spores 

 could be detected in the seed-coats. 



The tissues of the leaf, in the neighbourhood of young uredo-pustules, 

 frequently showed curious clumps of protoplasm in the cells, either free in the 

 cell-cavity, or attached to the primordial utricle, and looking like haustoria. 

 Eriksson assumes that we have here the key to the puzzle ; he regards these 

 * plasmatic corpuscles ' as the protoplasm of the fungus which, after leading a 

 dormant life commingled symbiotically with the living protoplasm of the cell, is 

 now gaining the upper hand and beginning to form a dominant mycelium. 



We are therefore to suppose that when the spores of rust, even if of the right 

 variety, alight on the tissues of a wheat-plant, it is a matter decided by external 

 and internal conditions whether the germ-tubes forthwith infect the plant and 

 grow out into a dominant, parasitic, sporiferous mycelium, as we know they 

 usually do, or simply manage to infect the cells with enough protoplasm to live 

 a latent symbiotic life for weeks — or even months — as a Mi/coplasma, which may, 

 under favourable circumstances, gain the upper hand, and grow out in the form 

 of a mycelium. 



This is a startling hypothesis, and brings us to the most advanced point along 

 this line of biological speculation. We must distinguish sharply and clearly 

 between such a view, which is by no means inconsistent with all we know of 

 parasites, so far as the dormant mycelium goes, and all the hazy, mystical sugges- 

 tions as to ' infective substance ' and so forth, which were so freely flung about 

 at the beginning of this epoch, and which De Bary's strictly scientific methods put 

 down so firmly. 



The idea of symbiosis is now comparatively old, and there are many cases of 

 dormant life now well established. Even the astounding notion of blended proto- 

 plasms can no longer be regarded as new. I need only remind you of (Jornu's 

 Rozella, which invades the thallus of Sajn'oler^ma, and Woronina in Vaucheria, 

 the protoplasm of the two organisms apparently blending and living a common life 

 for some time before the true nature of the parasite manifests itself. Eriksson has 

 avowedly been influenced by these and other cases among the Chrytridiaceee. 

 That the remarkable iutra-cellular fusions of Plasmodiophora and the now well- 

 established symbiosis of the organism of the leguminous root-nodules have also 

 had their influence on his work may well be assumed, and I think we may trace 

 also the efiectsofour knowledge of the latent life of Ustilago during the vegetative 

 period of the attacked cereal. 



