330 MINNESOTA BOTANICAL STUDIES. 



elongation of the embryo-sac and at the time of fecundation of 

 the egg the hyphae along the funicular region have ceased 

 growth, thus causing the isolation of a patch of hyphae between 

 the point of the attachment of the ovule and the micropvle. 

 This later becomes an infection-layer, for from this patch arise 

 those hyphae which penetrate the embryo. The hyphae do not 

 enter the embryo until the latter shows the rudiments of the 

 scutellum and growing point. As soon as the latter is estab- 

 lished hyphae grow from the infection-layer directly to the 

 growing point and by the time the grain is mature have built 

 up a patch of mycelium. Thus the mycelium passes from gen- 

 eration to generation of the host by direct infection and is appar- 

 ently able to dispense with spore formation. 



Since these facts were established I have attempted in various 

 ways, by altering the conditions of growth of the fungus to in- 

 duce it to form spores but all efforts have as yet failed. The 

 most obviously probable way of succeeding in this attempt 

 seemed to be the following. If the growth of the young embryo 

 were prevented the fungus might establish an extraordinarily 

 vigorous mycelium and in the absence of the embryo might 

 revert to the spore-forming habit, for it would seem probable that 

 the ancestral form might have formed its spores or a sclerotium 

 in the ovary. In one respect expectations were realized, for a 

 vigorous mycelium in the nucellus was produced. In fact the 

 hyphae were so densely compacted as to constitute a sclerotium- 

 like body ; but this was very small. Whether or not the fungus 

 inhibited the production of the normal amount of nucellar tissue 

 was not to be determined, but could now be ascertained since 

 plants with and plants without the fungus can be raised at will. 

 However the fungus refused to form spores. Two explanations 

 might be offered for this failure : (i) the habit of mycelial in- 

 fection may be so well established that ability to form spores 

 has been lost entirely ; (2) the fungus may be some ergot-form- 

 ing parasite or one which forms spores in some other organ 

 of the host plant. Analogy with other forms however indicate 

 the greater probability of the first proposition. 



As the development of some parasitic fungi seems to be 

 favored by weakness in the host plants, L. tcmulentum plants 

 with the fungus were partially starved by retention in dark 

 chambers for certain periods. It was hoped that the consequent 

 etiolation would favor the parasite at the expense of the host. 



