460 



RELATION TO ENVIRONMENT. 



are whirled along, often iniles awav In laic spring or early summer 

 the pods of the willow burst open, exposing the seeds, each with a tuft 

 of white hairs making a mass of soft down. As the delicate hairs dry, 



Toucli-me-not (Impatiens fulva) ; side and frtjnt view of flower below ; aho\e unopened 

 pod, and opening to scatter tlie seed. 



they straighten out in a louse spreading tuft, wldch frees the individual seeds 

 from the C(.>mpact mas?. Here they are caught b_\' currents of air and float 

 off singly or in smaU chmJs. 



895. The prickly lettuce. — Tn late summer or early autumn the seeds of 

 the pjrickh' lettuce (Lactuca scariola) are caught u]"i from the roadsides by 

 the winds, and cai-ried t<j lichls whi're the\' are iniliii.h.U-n as "well as unwel- 

 come guests. This phmt is shuwn in lig. 483. 



896. Tlie wild lettuce. — A related specie'^. the wild lettuce (I.actuca cana- 

 densis) occurs on roadsidi's ami in the borders ui fields, ami is about one 

 meter in height. The heads nf small yellow or juujtie flowers are arranged 

 in a louse or branchino; paidcle. The flowers are rather inccnispicuous, the 

 rays projecting but little abo\'(,- the apex ol the enveli.tping invttUicral bracts, 

 which closely press together, forming a fl(.)wcrdiead more t.)r le^s flask- 

 shaped. 



At the time of flowering the involucral bracts spread somewhat at the 

 apex, and the tips of the flowers are a little more prominent. As the flowers 

 then wither, the bracts press closely toocther again and tlie head is dosed. 

 As the seeds ripen the bracts die, and in drying bend outward and down- 

 ward, around the tluwer stem below, or they fall away. The seeds are 



