4i8 



DESIGN IN NATURE 



and organic forces both contribute to the dissemination of seeds. These forces are directed and controlled in the 

 operation. Nay more, the seeds, in many instances, are specially constructed to assist in the disseminating and 

 distributing process. 



One of the best-known examples of a volant or flying seed is supphed by the goat's-beard. 



The goat's-beard (Fig. 81) forms a typical parachute which for elegance of design and efficiency cannot be sur- 

 passed. It consists of an exquisite flattened disc sUghtly depressed in the centre ; the free margin being a little 

 turned up. It is supported in every direction by tapering structures, which radiate from a central point at regular 

 intervals (A). Between the radiating structures a most dehcate network of vegetable fibres resembling the finest 

 fihgree work extends ; imparting to the whole a delicate, gauzy appearance which indicates extreme lightness and 

 suggests the idea of flotation or flight. The radiating supporting structures display very graceful double curves ; 



B 



Fm. 81. 



Fig. 81. — The goat's-beard {Truiinpoyon jiratensis), as seen from above (A) and from the side (B). 



A. Goat's-beard from above. Shows the radiating supporting structures of the disc with a delicate network between. 



B. Goat's-beard from the side or in profile. Illustrates the parachute-nature of the goat's-beard. Natural size. 

 Drawn with special care from a fresh specimen in the Author's collection by C. Berjeau for the present work. 



Enlarged. 



those nearest the centre of the disc having their convexities directed upwards, those at the periphery or free margins 

 having their convexities turned downwards (B). 



Depending from the centre of the disc is a vertical portion or shaft, which may not inaptly be compared to 

 the stick or handle of an umbrella (B). This acts as a balancer, and so ensures the stability of the centre of gravity 

 of the seed whatever the direction of the wind. A more perfect arrangement for the waftage of the seed by the 

 wind to a distance cannot be conceived. As an example of " means to ends " it occupies a unique position, and 

 the aimals of botany will be searched in vain for a better example of design and the operation of a First Cause. 

 Here we have an instance of a structure, made in advance for the discharge of a special function. The structure 

 is in the highest degree striking, but the function to be discharged is by no means so obvious. The object of the 

 structure is, no doubt, to provide a surface which shall enable the wind to seize and waft the seed about until it 

 finds a suitable soil for planting itself. The seed is prepared for its flight by gradually becoming lighter as it ripens. 

 The function performed by the seed is passive (if any function can be so designated). The chief function is performed 

 by the actively moving wind. We have a structure exercising, as it were, no function. The structure and the 

 function, however, must be associated if any good is to result from the combination, and this can only be done by 

 enlisting the co-operation of the wind, which is the moving power in the present case. There is a dual arrange- 



