THE ANGIOSPERMAE 



1515 



of the variation curve of seed weight rises steadily from herbs of open 

 habitats to trees. 



Summary of the Data of Weights of all Types of Propagules 



The class intervals are arranged in ascending order from i to 24. The upper limit 

 of each class is twice that of the upper limit of the preceding class. (Class 3 — - 

 0-00000381 gm. to 0-00000763 gm. Class 24 — ^8 to 16 gm.) Salisbury and 



Fisher, 1942. 



The wings of seeds may be terminal either at one or both ends, like 

 those on Pinus seeds, or else surround the seeds (Fig. 1384), like the wing 

 of a samara fruit, such as that of Ulnuis. They are of all sizes, according to 

 the size of the fruit and seed, but the largest are those of the Cucurbitaceae 

 and Bignoniaceae. In Zanonia macrocarpa, a tropical cucurbitaceous 

 climber, the flat seed is surrounded by a fine membranous wing with two 

 lateral expansions, up to 10 cm. in diameter, which is the largest known. 

 I'he seeds float horizontally in the air like an aerofoil and describe elegant 

 spirals as they slowly descend, looking like large butterflies. 



Winged seeds are almost confined to woody plants. A few herbs, e.g., 

 Spergidaria, have small wing-like frills around the seed and many Iridaceae, 

 Apocynaceae and Cruciferae have thin, flat, light seeds, which are blown 

 about for short distances, even without wings. Linaria vulgaris, which is 



