JorUNAL OF THE DePA'KTMENT OF A(;RirULTURE. 



SOME COMMON ADULTERANTS FOUND IN 

 AGRICULTURAL SEEDS. 



By K. A. Lansdell, Division ui Botany, Pretoria. 



[This article is the tirst cif a series to be published descnbiug' the coiimidii imimritieis 

 in seed and how they can be recognized — Acting Editou.] 



There can he little doubt that nnuiy of the foreign weeds now found 

 in South Africa have lieen introduced into this country by the 

 nnportation of impure seed, also that the sowing of impure seed 

 is largely responsible for the spread of weed pests in the Union. 



Farmers frecjuently send in to this Division for determination 

 weeds which more often than not are asserted to have suddenly 

 appeared on the lands and were not noticed before. The usual 

 explanation is that they were introduced as impurities in seed which 

 had been sown. It is essential that farmers should see that the seed 

 they buy is free from such impurities. If this simple precaution is 

 taken in time, expense entailed in fighting the weeds will not only be 

 saved, but a better crop will result, as the growing w^eeds rob the soil 

 of moisture and mineral foods. Some of the common impurities 

 found in agricultural seeds are Dodder (Cuscufa spp.), Burw^eed 

 (Xanthiinn sinnosum), Cockle-bur (Xanthium spp.), the Malta Thistle 

 (Centaurea iiieliteiisis), the Spear Thistle (Cnicus lanceolatus), Star 

 Burr {AcantJiospermum spp.), Mexican Poppy (Argevione Mexicana), 

 Khaki Weed {Alternanthera achyrantJia), and the Dwarf Marigold 

 (SchkuJiria honariensis) . 



The most dangerous imparity of clover seed is that of dodder. 

 If dodder is introduced into a lucerne crop and allowed to ripen its 

 seeds the ground may become infected for at least five to Xi'^n years. 

 Superficially the seeds of many weeds resemble those of the assi ciated 

 agricultural crop seed so closely that a sample or seed must l)e 

 examined carefully if the impurities are to be detected. In ]iiaking 

 an analysis of seed, first of all the contents of the bag or c'ifferent 

 parts of the bulk should be emptied out and thoroughly mixed. A 

 small sample is then taken from the top, middle, aiid l)ottom of the 

 receptacle containing the seed. These three samples are mixed und 

 spread on a sheet of white paper and carefully examined. The aid 

 of a simi)le magiiifying gla.ss will be found useful in many cases. 

 With a needle or some other pointed instrument separate the impuri- 

 ties from the good seed. By weighing the impurities and com- 

 paring tiie weight with the samph^ a rough estimate can be made ot 

 the total weight of impure seed in the bulk of the sample. 



Dodder in Lucerne. 



Plate I, figs. 1 and 2 ; Plate II, figs. 1 and 3. The seed ot Dodder is 

 spherical or oval in shape, greyish or yellowish-brown in colour, and 

 the surface is slightly rough. It resfiiihlfs Ihe lucerne seed vei'y 

 much, but the latter is l;trg*er and l\i(liu\v-sha])e(l. 



