i8o FLOWERS OF WASTK PLACES, ETC. 



expelled from ihc pod b)- ;ui clastic muvcnieiU, and arc drawn into die 

 crround bv a similar hy<Troscopic arrangement. The carpels do not open 

 biit are contracted with the seeds still enclosed, the awn remaining 

 attached. The layers of the cell-wall consist of lamelke of different 

 densities and refractive indices. In the one the cells are elongate and 

 woody in concentric series, being light and dark alternately. These 

 last are the edges of the lamelke. The parallel lamella- in two .series 

 are inclined to the axis at different angles, or wind spirally in opposite 

 directions around the lamelkt. The expansion of the cell-wall tissue 

 during imbibition is caused by the swelling of the striae of less density, 

 antl the imbibition of the water in all probability sets up spiral tension, 

 producing a twisting motion. Further single cells roll up as shown 

 by Francis Darwin. Or the twisting of the awn may be tlue to the 

 difference between the contraction of the woody fibres and the com- 

 paratively soft parenchyma or thin-walled cellular tissue, in which the 

 cells are not much longer than Ijroad. The more complete lignifica- 

 tion of the outer cells, which contract more than the inner, may be 

 the reason, the spiral twisting being due to the curving of the woody 

 bars with the hollow side upwards. JMoistness regulates the amoimt 

 of the twisting of the awn, which twists and untwists with variation in 

 atmospheric humidity, being thus hygroscopic. The fixing of the awn 

 during the process of untwisting causes the seed to be driven into the 

 ground. The .seed ve.ssel is so sensitive the arista or awn curls up 

 under the influence of the heat or moisture of the hand. The elastic 

 movement of the seed to promote dispersal is one of the most inter- 

 esting examples oi sensitiveness. 



Stork's ]')ill is almost entirely a sand plant, growing almost always 

 on sand soil. By the sea-coast it is a halophyte, living on a saline soil. 



The Brown Argus i^Lyccena astrarche) feeds upon it, also Geotomus 

 pnnctii/atits -AWiX Hctcrogaster tirticer, Hemiptera Heteroptera. 



Erodiiini is from the Greek Erodios, a heron, in allusion to the 

 shape of the fruit. Cicittariuni is from cicitia, hemlock. Itecause the 

 foliage resembles that of hemlock. The plant is called Wild Musk, 

 Fink or Fowk Needle, Stickpile. 



EssENTi.M. Specific Cii.\racters: — 



69. Eroduim cicutariuvi, L'Herit. — Stem jirostrate, spreading, 

 downy, leaves pinnate, leaflets .sessile, pinnatihd, stems many-Howered, 

 flowers lilac, in umbels, stipules lanceolate, stamens dilated. 



