' 

 RHEOTROPIC REACTIONS OF PLASMODIA 69 



the gelatine and the plasmodium will be found to move to- 

 ward it. 1 



106. Rheotropic Reactions of Plasmodia. Secure specimens of 

 plasmodia growing on leaves or decaying wood as in 103 and 

 bring into the laboratory with as little disturbance as possible. 

 Lay the material on the bottom of a flat dish. Arrange a beaker 

 of water near by, and place a strip of filter paper with one end 

 in the water and the other brought over the side of the beaker 

 and resting on the material near the plasmodium. The plas- 

 modium will be found to move toward and upward along the 

 filter paper. It is attracted or stimulated by the current of 

 water, and responds by moving against it. The mechanism by 

 which this is accomplished is not easily explainable. The above 

 test should be made in a dark room to avoid phototropic reactions. 



107. Influence of Water and Water Va- 

 por on Form. The long continued expo- 

 sure of a species to a habitat rich in mois- 

 ture, or to arid conditions will result in 

 adaptations suitable to the endurance of 

 these water relations. The change of a 



plant from a land to an aquatic habitat re- 1 



suits in finely divided or ribbon-shaped ^' ^ 



leaves, while the species living in arid re- FlG - 2 9- Lcaves of Ra ~ 



nunculus delphinifolius: W, 



gions may develop thick succulent foliage growing submerged in the 

 or other forms suited to the storage or water : Z, growing from the 

 conservation of the limited water supply, portion of the stem above the 



surface. After Goebel. 



These outward changes in form are ac- 

 companied by many internal adaptations. Many species are so 

 elastic that they are capable of producing organs adapted to ex- 

 treme conditions on the same individual. 



108. Form and Structure of Organs in Water and Watery 

 Vapor. Grow seedlings of corn for a week in a germinating dish 

 and ascertain the average measurements of the root-hairs and 



1 Ayers, H. Methods of study of the Myxamoebae and the plasmodia of the My- 

 cetozoa. Jour. f. Applied Microscopy, x : I. 1898. 



