42 LOUISE DOSDALL 



(5) ADAPTATIONS 



That Equisetum fluviatile is a very stable form is proved by 

 the fact that no structural differences could be discovered in 

 cross sections of the stems growing in the different water con- 

 tents. The epidermis was also studied for differences in the 

 number of stomata ibut the average number per square millimeter 

 did not vary. 



The results of adaptation experiments were entirely negative. 

 No structural differences could be discovered in the epidermis 

 chlorenchyma, vascular tissue, or air space from the cross section 

 of Equisetum fluviatile which had grown in the varying water 

 contents, from November, 1916, to April, 1917, in the green- 

 house. Sections of epidermis were also studied for the number 

 of stomata but the average per square millimeter did not vary. 

 These results correspond with those of E. S. Clements (1905: 87) 

 who found no variation in certain xerophytic forms grown under 

 varying conditions of water content. 



IV. SUMMARY AND CONCLUSIONS 



1. The results of the present investigation of the water re- 

 quirements of Equisetum fluviatile show that this species requires 

 a higher concentration of water in the soil in order to maintain 

 its normal functions. The amount of water remaining in the 

 soil at the death of the plant is greater than the amount at the 

 death of Ranunculus sceleratus. When growing in the same soil 

 mass with Helianthus annuus and Phaseolus vulgaris, Equisetum 

 wilts first. A comparison of the transpiration shows that the 

 water loss is much greater than from the mesophytes and the 

 xerophytes with which it was compared. Equisetum fluviatile is 

 therefore to be considered a true hydrophyte. 



2. The high transpiration is correlated with low photosynthetic 

 efficiency as compared with Helianthus annuus and Phaseolus 

 vulgaris. 



3. The difference in the time of wilting between Equisetum 

 and the mesophytes with which it was compared shows that the 



