190 



BRITISH PLANTS 



sorrel. The~ horse-chestnut forms a curious kind of cap- 

 sule. Its ovary is composed of three carpels, and is three- 

 chambered, with two seeds in each chamber. But one 

 seed in one chamber alone develops ; the others abort. 

 Two of the chambers are crushed out by the pressure of 

 the successful seed, and the result is a one-seeded fruit. 

 Occasionally two seeds share the food 

 between them, and we get a two-seeded 

 " nut." When ripe, the outer shell, 

 which is thick and succulent, splits apart 

 into three pieces, and the seed is released. 

 3. Sehizocarps (Gr. schizo, I split), or 

 separating-fruits, are derived from syn- 

 carpous ovaries formed from two or more 

 carpels. There are usually as many 

 chambers as there are carpels, with one 

 seed in each. When the fruit is ripe, 

 the carpels separate from each other into 

 a number of one - seeded indehiscent 

 sections (mericarps : Gr. meros, a part). 

 Each of these is biologically an achene. 



In the maple and sycamore (Fig. 94) 

 the fruit consists of two or three winged 

 carpels, which ultimately separate into 

 one - seeded portions. It is a double 

 samara, or key. The fruit generally 

 leaves the tree whole, forming a kind of 

 shuttlecock, which spins round in the 

 wind and describes a zigzag course in its 

 descent. 



In the geranium five carpels split 

 away from each other and from a column 

 which is an upgrowth of the receptacle. 

 In the cultivated geraniums (Pelargon- 

 ium), the style forms a curved awn set 

 with a fan of silken hairs. In the wild 

 geraniums, or crane's-bills (Geranium), the hairs are absent, 

 and the mericarps break away from the column with 

 such force that in some species (G. Robertianum, G. 

 lucidum, G. phceum, G. molle, and G. pusillum) the seeds 

 are actually shot out of their carpels ; the mericarps are 

 then known as cocci. In the stork's - bill (Erodium, 

 Fig. 95) a spirally- twisted awn is provided with a fan of 



FIG. 93. SELIQFA 



OF MUSTARD, 

 SHOWING THE 



Two VALVES 

 SPLIT AWAY 

 FROM CENTRAL 

 PARTITION. 



