874 



THE DISPERSION OF SPECIES BY MEANS OF FRUITS AND SEEDS. 



With this curious form of fruit we may associate those in which the claws or 

 hooked prickles are metamorphosed branches, or parts of abortive flowers situated 

 on special ramifications. It will be sufiicient to adduce two examples of this group, 

 viz., Pupalia atroiovurpiirea, of the family Amaranthacese, and Pteranthus echinatus 

 (see fig. 478 '') of the family Paronychiacea3. In Pupalia atropibrpiirea short 

 branchlets spring from the axils of the bracts; a few of them bear fruits, whilst the 

 majority are modified into hooked prickles and form a tuft which easily fastens on 

 to foreign bodies, and becomes detached from the main axis. Pterantkus echinatus 

 has several short branchlets in each inflorescence situated close to the fruit, and 

 bearing at their extremities abortive flowers with hooked sepals. 



Fig. 479.— Fruits which hook on to or stick into passing objects. 



1 Carex mieroglochin. 2 Single fruit of the same, s Galium retrorsum. i A piece of the stem of the same. « Carex 

 Pseudocypencs. 6 Single fruit of the same, r Triglochin palustre. « Single unripe fruit of the same. » Transverse 

 section through the same fruit, lo Single ripe fruit with its component valves separated. ", *, 6, s, 9 and lo magnified. 



All the clawed or prickly fruits and clusters of fruit above enumerated 

 easily come away from the mother-plant when pulled by the objects to which they 

 have attached themselves. But there are other cases where the hooks and claws are 

 firmly attached to the axis of the plant as a whole, so much so indeed that if the 

 object to which they are fastened gives a pull a large piece of the stem is torn away, 

 and sometimes even the entire plant is uprooted and carried bodily away. To this 

 class belong the fruits of several Rubiacese, of which Galium retrorsum (see figs. 479^ 

 and 479 *) may be taken as a type. The fruit-bearing stem of this plant is at once 

 broken off* or uprooted when its barbed bristles catch in the coat of a passing animal. 

 The species of the genus Uncaria also are examples of the kind. The long, creeping 

 stems develop here and there clusters of fruit and at other spots abortive peduncles, 

 which are metamorphosed into strong, sharp claws. When these claws get hooked 

 to an animal's foot, a more or less large piece of the stem is torn away, and with it 



