AN OUTLINE OF PHYTOBIOLOGY. 15" 



harder upon the smooth seeds between them until these are 

 suddenly and swiftly ejected as one shoots a bean or nut from 

 between the fingers, as in some stemmed violets. Or the styles 

 may ripen on an elongated receptacle forming springs to hurl 

 away ovary or seeds as in the genus Geranium. Or the carpels 

 under spiral tension burst all apart from one another as in many 

 Euphorbiacete, in some cases as the castor bean, or better the 

 West Indian " sand box," bursting with a loud report and 

 hurling the seed many feet. Or two-valved pods may split 

 suddenly by the independent rolling up of the two valves, as in 

 some vetches and lupines. 



3. Soft fruits may become strongly turgescent, i. e., gorged 

 with water in their inner and dry on their outer parts, until 

 finally they explode at the weakest point and shoot out the seed- 

 This happens in fruits with valves, in which case the latter 

 usually suddenly curl up and throw off" the seed, as in 

 Impatiens, a^nd many Crucifeme, or the entire pulpy interior may 

 become turgescent under a firm skin, as in some Cucurbitacea?. 

 In the " squirting cucumber" of the Levant, pulp and seeds are 

 shot through the opening left where the fruit drops from the 

 stalk, wliile in Cydanfhera it bursts along the sutures. 



The power of ripening tissues to produce movement is 

 also used to assist seeds in self-planting, and to aid 

 locomotion by the production of tumble-weeds and to 

 form elastic stalks, all presently to be described. 



IV. Locomotion hi/ Utilization of Air Currents. 



Of all of the locomotive forces of Nature, air currents 

 are the most universally prevalent and easily atilizable. 

 They are of all grades, from the barely perceptible up-and- 

 down convection currents of still warm days to great gales. 

 To effect by them a movement from place to place, it 

 is simply necessary to develop about the seed structures 

 which will spread as great a surface as possible in 



