876 



THE DISPERSION OF SPECIES BY MEANS OF FRUITS AND SEEDS. 



may take those of Garex pauciflora and TriglocUn palustre (see figs. 479 1> ^■^' ■ ' ) 

 These fruits are borne on a stiff, erect axis, and when ripe are pointed obliquely 

 downwards. They easily become detached from their stalks and are left sticking 

 like needles in the skin or fur of animals that touch them. 



Straight or slightly curved bristles and prickles may take part in another way 

 in the dispersion of fruits. When they are set in rows like the teeth of a comb on 

 the surface of a fruit or stand out in pairs from it, as, for instance, in Gwrex 

 Pseudocyperus (see figs. 479^ and 479 «), the woolly hairs and delicate feathers of 

 some animals are liable to get entangled in them, and they are then dragged from 

 their stalks. The same thing happens where the prickly processes projecting from 

 the fruit cross one another, as in Pterococcus, Sycios, and many species of the Medick 

 genus (e.g. Medicago eiliaris, M. littoralis, M. sphcerocarpa, M. Untaculata, and 

 M. tribuloides), and where the surface of the fruit or of the fruiting calyx is 

 covered with stiff bristles forming acute angles with it, as in Asperugo, Myosotis, 

 Pcurietaria, PhysocauUs, and TariUs (see figs. 477 1". n. i^). In many Grasses the 

 awns which project from the backs of the glumes act. as instruments for catching 

 the hair of animals as they pass, and the latter is also liable to get caught between 

 the nut and the hardened perianth-segments which surround it in several Chenopo- 

 diace^. It is not necessary for this that the bristles, prickles, or awns should be 

 pointed, but it is advantageous for their surfaces to be rough or jagged, as in Torilis 

 (see fig. 477 ^^). We must not omit to mention also that the tufts of hair which 

 clothe some fruits and seeds, and act as parachutes and wings, often get entangled in 

 the hair or feathers of animals, and thus play an additional part in dissemination. 

 The rough coats of sheep, goats, oxen, and horses are always found to have such 

 hairy fruits and seeds affixed to them after they have passed over ground on 

 which herbaceous Composites, shrubby Willows, &c., grow at the season when those 

 plants are in fruit. I have myself removed from the coats of animals of the above- 

 mentioned kinds fruits and seeds of Anelnone sylvestris and of various species of 

 the genera Galamagrostis, Grepis, Gynanchmn, Epilobium, Eriophorum, Lactuca, 

 Lagcecia, Micropus, Populus, Scdix, Senecio, Sonchus, and Typha. 



Anyone who has forced his way through a thicket of poplars and willows in 

 early summer or through a clearing overgrown by Galamagrostis, Epilohium, and 

 Senecio in late summer can bear witness to the manner in which fruits and seeds of 

 the sort in question adhere to the clothes. Sticky and hooked fruits are also found 

 upon one after such excursions, and it is perhaps not superfluous to remark that 

 what has been said concerning the dispersion of seeds by animals must be taken to 

 apply also to dissemination by men. Of course we are here referring to uninten- 

 tional dissemination by human agency. We are here concerned with the cultivation 

 of corn, vegetables, garden-flowers, edible fruits, forest-trees, &c. — i.e. with the 

 purposeful dispersion of plants by men — in so far as many of the species in ques- 

 tion establish themselves beyond the limits of the fields or gardens, where they have 

 been sown or planted by man, through the operation of their natural means of dis- 

 semination and without human assistance, and further, inasmuch as weeds are often 



