ATTACHMENT-ORGANS OF SEEDS AND FRUITS 207 



branches of trees. Here each member of the tuft of silky hairs which 

 acts as the parachute-organ of the seed terminates in a pointed, thick- 

 walled and sharply recurved hook. By means of these grappling-hooks 

 the seed is enabled to adhere to the thin and often slippery twigs which 

 the plant inhabits. In the case of an epiphytic Orchid, also (Phygma- 

 tidium), the same observer found both ends of the minute cylindrical 

 seeds to be furnished with a number of 

 hooked processes. 



Some account must next be given 

 of the exceedingly diversified hook- or 

 claw-shaped attachment-organs that assist 

 in the dispersal of seeds and fruits, by 

 fixing these structures to the fur or 

 plumage of animals. The morphological 

 value of such hooks cannot be con- 

 sidered here ; the simplest of them re- 

 present trichomes. Anatomically they 

 all agree in the thick-walled character 

 of their constituent cells, which some- 

 times indeed consist of typical stereides. 

 A few examples must suffice to illustrate 

 the interesting and varied forms assumed 

 by these organs. 



In the case of Circaea lutetiana 

 hooked unicellular thick-walled hairs 

 assist in the dispersal of the fruits. 

 Each hair has an expanded foot or base 

 which is surrounded by a rosette of 

 epidermal elements. Unicellular hooked hairs also occur on the pales 

 of Ztqjpago racemosa (Geamineae) ; here the body-cell of the hair has 

 its more or less attenuated base deeply embedded in a cup-shaped 

 multicellular pedestal (Fig. 78). 



In Caucalis daucoidcs (Umbellifeeae) the rnericarps are covered 

 with hooks about 2"5 mm. in length ; each hook consists of a slender 

 tapering bundle of thick-walled prosenchymatous stereides, the whole 

 being surmounted by a single very large transversely directed cell bent 

 in the shape of a f (Fig. 79). The distal end of this terminal cell, 

 which acts as a barb, is sharply pointed, and so thick-walled that its 

 cavity is reduced to a narrow slit. The wide proximal portion of the 

 lumen contains the remnants of a massive protoplast. The wall abutting 

 against the bundle of stereides is moderately thickened and provided with 

 numerous pits. In the Burdock (Zappa major) each of the numerous 

 hooks of the involucre consists essentially of a tapering, distally recurved 



Pio. 78. 



Hooked hair from a pale of Lappago 

 racemosp. 



narrow, radially 



elongated 



