^50 THE DISPERSION OF SPECIES BY MEANS OF FRUITS AND SEEDS. 



developed flowers in the cluster growing at the end of the flower-stalk, whilst a 

 number of abortive flowers are crowded together in a tuft in the middle of the 

 inflorescence. At the season when the legumes are formed from the fertile flowers 

 the calyx-teeth of the abortive flowers increase in size and assume the shape of long 

 hairy bristles, which bend over outwards and form a loose globular inclosure round 

 the head of leguminous fruits. These balls afterwards become detached from the 

 stalk and are rolled away by the wind. 



Even entire plants are in some cases uprooted or have their stems severed from 

 the roots at the base in the fruiting season, and are then rolled along like balls by 

 the wind. The most remarkable instance is that of Plantago Gretica, which is 

 shown in fig. 465. This is an annual plant possessing an abbreviated main axis from 

 which springs a tuft of stiff", erect flowering stems. When the fruits begin to ripen 

 the stems curve down in coils to the periphery of the plant, and by so doing give a 

 strong pull to the abbreviated axis and to the simple tap-root, which is inserted in 

 the earth in a vertical position. The soil on which Plantago Gretica grows being 

 completely dried up in summer is full of cracks, and the pull imparted in the 

 manner described is in consequence sufficient to uproot the plant. The plants 

 now in the fruiting stage have the form of flattened balls and are very light, so 

 that the entire structure is rolled along by gusts of wind. Plantago Gretica is also 

 a type of the so-called " Steppe- witches " and " wind- witches ", which are a source 

 of so much wonder to travellers in the regions of Steppes. On the high table-land 

 of Persia there is a plant named Gundelia Toiirnefortii which grows in loose, round, 

 prickly sods, and has a tap-root deeply sunk in the earth. When the fruits are ripe 

 the neck of the root rots away and the round sod then rests simply with its stiff 

 lower branches in contact with the ground. Whenever the slightest wind begins to 

 blow innumerable quantities of these sods are set in motion, and are thus dispersed 

 over the plateau. The herbaceous plants of the Steppes of Southern Russia which 

 exhibit the phenomenon of a decay of the bases of the stems in the fruiting season 

 and a consequent liberation of the dry aerial portion of the plant belong to families 

 of the most various kinds. The most common are Alhagi camelorwtn, Gentaurea 

 diffusa, PIdomis herba-venti, Rapistrum perenne, and Salsola Kali. It often 

 happens that a number of these dry, branching herbs get hooked and entangled 

 together as they roll along, until at length they form a ball as big as a cartload of 

 hay. Such balls have also been seen lifted up by whirlwinds and driven bounding 

 over the plain. It is not surprising that this marvellous phenomenon has appealed 

 to the imagination of the inhabitants of the Steppes, and has even become a subject 

 for witch-lore whence have arisen the names Wind- witch and Steppe-witch. 



It only happens in a small proportion of these cases of rolling fruits, wind- 

 witches, and the like, that the seeds are strewn out as they are bowled along; when 

 this does occur it is usually occasioned by some unevenness in the ground which 

 gives a sudden jog to the rolling body. In the majority of cases the seeds do not 

 escape until the fruits a,re brought to rest by encountering some insurmountable 

 obstacle, the reason being that the seed-vessels only open when they become wet. 



