56 



The study in the field brought out a number of points of in- 

 terest, but failed to reveal any sufficiently conspicuous differences 

 between the swamp and bog plants. The form of the rhizomes 

 and roots seemed to be essentially identical, whether the plants 

 were growing in sandy or loamy swamps, or in the muck of bogs. 

 The conditions which caused death of the rhizomes, viz., too 

 great a piling up of sand or debris above them, obtained in both 

 cases. Within limits, the Iris rhizome can adjust itself to 

 changes in the soil level by growing up or down. The limit in 

 the case of encroaching sand seems to be about 20 to 25 cm. 

 Excellent examples of this were to be seen in the spring of 1922, 

 following the unusually heavy icework of the winter of 1921-22 

 at the head of Burt Lake. Approximately 8 meters of the beach 

 was shoved in on the swampy area at the head of the lake. 

 This covered large beds of Iris with about 45 cm. of sand and 

 killed the plants. Decayed rhizomes were found beneath the 

 sand where Iris had formerly been abundant. 



In general the characteristics of the stems and leaves appeared 

 to be essentially identical throughout — the modifications which 

 occurred in the leaves being due primarily to the amount of 

 shade the plants were receiving. As shade was more frequently 

 met with in bogs, particularly the higher-shrub bogs, greater 

 etiolation of the leaves was more frequently met with there. 

 Similar conditions in swamps however produced the same re- 

 sults. The only feature of difference was that the leaves from 

 bog plants averaged a trifle narrower than those from swamps 

 (1.8 cm. in bogs, 1.9 cm. in swamps). A study of free-hand 

 sections of the leaves failed to reveal any differentiating char- 

 acters, but in the rootstock it was found that the epidermal cells 

 of the plants growing in bogs had very much thicker walls than 

 those growing in swamps, (19 [j. in bogs, g [i in swamps). In 

 bogs, fruit was much less abundantly produced and the capsules 

 that formed were small. 



In conclusion, it would appear from this study, that in the 

 case of Iris versicolor L. in the Douglas Lake, Michigan region, 

 the visible effects of the bog environment upon this swamp 

 plant were a slight narrowing of the leaves, a very conspicuous 

 thickening of the cell walls of the epidermis of the rhizome, and 

 a reduction both in the amount of fruiting and in the size of the 

 fruit. 



