George Raymond Gage 25 



field. Some few additional spores, however, probably do get inside of 

 the glumes when the oats are being threshed. By placing oats in a bag 

 along with U. If vis spores, very little shaking is necessary to bring about 

 such a condition, especially in oats the kernels of which are not tightly 

 enveloped by the glumes, or in those with the glume tips broken off. 

 With glumeless varieties, the spores may reach the naked kernels in 

 large quantities at threshing time. Since very few of the spores of U. 

 h vis are disseminated in the field, this inoculation at threshing time 

 would exceed that from the same process with U. avi nae, in which very 

 few of the spores are not disseminated in the field. 



It is evident, therefore, that these observations confirm those, of pre- 

 vious investigators, but perhaps greater emphasis may now be laid upon 

 the differences existing between the inoculation processes in the two 

 species. 



Incubation studies 

 With Ustilago avenae 



As has been stated, those spores of U. avenae that lodge on the stigma 

 and the ovary in the glumed oats germinate in a very short time. Those 

 on the stigma, due to the excretions thereon, give rise to germ tubes 

 sooner than do those on the ovary Avails, but under the weather condi- 

 tions prevailing at the time of the writer's observations the majority of 

 the spores were fully germinated at the end of five days. Xo sporidia 

 were formed, a result which may be explained by unfavorable tempera- 

 ture relations as brought out by Arland. 



Penetration of the glumes and the epidermis of the pericarp was evi- 

 dent. By removing the pericarp epidermis and staining with cotton 

 blue, the developing germ tubes could be found in all stages. Some 

 were found outside, some were entering the cells, and some which had 

 penetrated through the cells were established between the epidermis and 

 The adjoining tissues. As is well known, in the development of the cary- 

 opsis certain tissue changes take place in the inner part of the pericarp 

 when it is fusing with the integuments of the ovule. The writer is of 

 the opinion that the mycelium passing through the epidermis of the 

 pericarp is favored by these changes. Careful examination of the ma- 

 terial (Plate I, 2) brings out this point. The mycelium, once it has 

 passed through the epidermal cells, seems to grow and spread very rap- 

 idly, and it appears as if no interference takes place by intervening 

 cell walls. 



With glumeless oats, the incubation process for those spores whicL 

 reach the ovaries at blossoming time is exactly the same as with glumed 

 oats. In addition, as is brought out later in the discussion of epiphytol- 

 ogy, those spores which reach the caryopsis in the field after pollination 

 also germinate in a very short time and produce mycelium which in- 



