Weeds of South Africa. 541 



WEEDS OF SOUTH AFRICA. 



By K. A. Lansdell, Botanical Assistant, Division of Botany, 



Pretoria. 



[Like- other countries, Soutli Africa is awaking to the importance of 

 suppressing its noxious weeds which, owing to the alarming rapidity of their 

 spread in recent years, are becoming increasingly dangerous to our pasturage 

 and wool and other agricultural pursuits. While much has been done in the 

 pa^t to place the farmer in a position to recognize and cope with the danger, 

 the problem grows in seriousness, and the time has arrived when all informa- 

 tion regarding the noxious weeds found in the LTnion should be gathered into 

 one publication for the use of the farmer, the student, and the general public. 

 This work has now been undertaken by the Division of Botany, the opening 

 contribution, continued hereunder, appearing in our April, 1921, number. This 

 publication, which will include an illustrated glossary on the morphology of 

 weeds, is the first of its kind in South Africa, and will appear in serial form in 

 the Journal. — Editor.] 



II. 



Leaves. 



The leaves are borne on the stems at the nodes. They are organs 

 of respiration, transpiration, and assimilation, i.e. it is through the 

 leaves that the plants breathes, gives off water-vapour, and in which 

 the carbon dioxide of the atmosphere is elaborated into complex 

 compounds. 



A typical leaf is composed of a flattened blade or larnina, and a 

 petiole or leaf stalk, which attaches the leaf to the stem. In many 

 leaves stipules are present which are appendages on each side of the 

 leaf insertion. (See fig. 12.) 



The leaves may be arranged on the stem in the following 



manner 



Opposite, when two leaves arise at the same node on opposite 

 sides of the stem, e.g. the Upright Star-bur 

 (Acanthospei'Tnuvi hispiduTti) , etc. (See fig. 13.) 



Alternate, when the leaves are scattered on the stem, e.g. the 

 Malta Thistle {Centaurea Tnelitensis) , etc. (See fig. 14.) 



Sessile, when the leaves have no leaf-stalk as young leaves of 

 the Upright Starbur (AcanthosperTnum hispiduTn). (See 

 fig. 13.) 



P etiolate, when the leaves are attached to the stem by a leaf- 

 stalk called the petiole, e.g. the Pig Weed (ATnaranthus 

 paniculatus) , the Burweed (Xanthiuvi spinosmn), etc. 

 (See fig. 16.) 



