INTROGRESSION IN IRIS 9 



all held so stiffly upright as on a typical HGC. The H-1 

 group was a brilliant mixture. It varied from plants looking 

 more or less like HGC to others resembling the artificial Fi 

 to a few others more like Fulva. The flowers were large on 

 some plants, small on others. Petal and sepal shape differed 

 from plant to plant. The colors ranged from deep blue to 

 red, with many variations in the size, shape, color, and pubes- 

 cence of the signal patch. The spot at which this hybrid 

 swarm was growing was the abandoned bed of the old deltaic 

 stream. On this particular farm the land had mostly been 

 cleared, and then a second-growth woodland had been al- 

 lowed to come up in the depression. This had again been 

 cut over heavily, and the whole area had been overpastured. 

 So many cattle had been kept on the area that the shrubs 

 in the swamp had been browsed. There was much bare soil 

 and relatively little grass, and in the softer ground of the 

 swamp the cattle had created '^ buffalo wallows" by their 

 attempts to get through in wet weather. On the adjoining 

 farms the overpasturing was not so evident. The woods on 

 one had been almost entirely cleared from the depressions 

 and replaced by a healthy stand of grass. On the other, the 

 second-growth woodlot had been preserved with little cutting 

 over and very little pasturing. 



These facts are described in such detail because this par- 

 ticular case is a really critical experiment for understanding 

 the d^mamics of hybridization. The bizarre hybrid swarm, 

 H-1, was entirely limited to this greatly disturbed area. On one 

 side the hybrid plants went up to the very fence line of the 

 adjoining property but no farther. On the other side they 

 did not quite extend to the fence line. In this little bit of 

 repeatedly cut-over and heavily pastured woodland, ad- 

 jacent to the spot at which the two species were in contact, 

 there were many more hybrids than in all the rest of the vi- 

 cinity put together. The reasons for this connection be- 

 tween the disturbance of the habitat and the results of hy- 

 bridization will be discussed in the next chapter; for the 

 present it needs to be pointed out merely that such a con- 



