318 



JOL'R^"AL OF THE DEPARTMENT OP AGRICULTURE. 



Ihe stem elongates and produces flowers and seeds, and so completes 

 the life- history, e.g. the Spear Thistle {Cnicus lanceolatus), St. Mary's 

 Thistle {SilybuTn marianum). 



Perennial Weeds produce roots, which send up flower-stalks year 

 after year, and such weeds may exist for an indefinite period, e.g. the 

 Canada Thistle {Cnicus arvensis) and the Prostrate Star-bur (Acantho- 

 spermum xanthoides). 



HAVSTORIA'^] 



STEM OF DODDER 



(iNLiSCiC) 



Fig. 6. — (1) Stem of "'Dodder" QCu.scnfa sp.), showing haustoria. 

 (2) Portion of stem with haustoria enlargctl. 



The following table gives the duration of twelve noxious weeds 



Common Name. 



Scientific Name. 



Type of Weed. 



The Morphology of Weeds. 

 Seeds may be of different sizes and shapes, and their surface may 

 also vary considerably. Each species of plant has seeds which are 

 constant in almost all respects for that species. The seed consists of 

 the following parts: (1) one or two seed-coats, and (2) the embryo. 

 The embryo is divided into (a) two cotyledons : leaves which contain 

 nourishment for the young plant ; (6) the radicle or future root ; and 

 (c) the plumule or shoot. 



