MIGRATION 47 



(b) TurgescencG, edoboles {Oedobolae, oiSos, to, swelling). 

 Dissemination by turgescence is highly developed in 

 Pilobolus and in Discomycetes, though in the latter turgescence 

 results rather in placing the spores in a position to be 

 readily carried by the wind. Impatiens and Oxalis furnish 

 familiar examples of fruits which dehisce in consequence of 

 increased turgidity. 



(o) Dessication, xerioboles {Xeriobolae, ir/pia, ^, dryness). 

 The number of fruits which dehisce upon drying is very 

 large, but only a small portion of these expel their seeds 

 forcibly. Geranium, Viola, Erysimum, and Lotus illustrate 

 the different ways in which dessication effects the sudden 

 splitting of fruits. 



(d) Resilience, tonoboles {Tonobolae, toVos, 6, a stretching 

 or tension). In some plants, especially composites, labiates 

 and borages, the achenes or nutlets are so placed in the per- 

 sistent calyx or involucre that the latter serves as a sort of 

 mortar for projection, when the stem of the plant is bent to 

 one side by any force, such as the wind or an animal. It 

 will be noticed that two separate agents are actually con- 

 cerned in dissemination of this sort. 



Frequently, two or more agents will act upon the same 

 disseminule, usually in succession. The possibility of such 

 combinations in nature is large, but actual cases seem to be 

 infrequent, except where the activities of man enter into the 

 question. Some parts, moreover, such as awned inflor- 

 escences, are carried almost equally well by wind or animals, 

 and may often be disseminated by the cooperation of these 

 two agents. The wind also often bluws seeds and fruits into 

 streams by which they are carried away, but here again, 

 parts adapted to wind -dissemination are injured as a 

 rule by immersion in water, and the number of plants 

 capable of being scattered' by the successive action of wind 

 and water is small. 



In the present state of our knowledge of migration, it is 

 impossible to establish any definite correspondence between 

 dissemination-contrivance, agent, and habitat. As a general 

 rule, plants growing in or near the water, in so far as they 



