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NOTES ON THE MORPHOLOGY AND BIOLOGY OF 

 HYDNOBA AFBIGANA Thunb. 



By R. Makloth. 



(Read November 28, 1907.) 



The genus Hydnora, which comprises several species (about 

 seven), is confined to Africa, Bourbon, and Madagascar. They are 

 all parasites, which grow on the roots of different shrubs and trees. 

 The species which forms the subject of these notes, viz., Hydnora 

 africana, uses the common milkbush of the karroo and karroid 

 regions of the interior as its host, viz., Euphorbia mauritanica L. 



The genus is usually placed in the natural order Ramesiacese, 

 which in its turn is sometimes combined with Cytinaceae, as, e.g., by 

 Bentham-Hooker. It has been pointed out, however, by Solms- 

 Laubach that the connection, as far as the morphological characters 

 are concerned, is a very weak one, and that it would be better to 

 establish Hydnoracese as a separate order. There is only one other 

 plant nearly allied to Hydnora, viz., the South American genus 

 Prosopanche, which is monotypic, possessing only one species, viz., 

 Prosopanche Burmeisteri De Bary. This plant represents one of the 

 few threads which connect the flora of South America with that of 

 South Africa. 



There are three species of Hydnora known from South Africa, but 

 one only, viz., H. africana, is of fairly common occurrence. 



The plant consists of an underground angular stem, which is 

 covered with tubercles, but produces no roots, attaching itself to the 

 roots of the host by sending suckers into its tissue. At these spots 

 the Euphorbia root swells considerably, and as the free end usually 

 dies, such a root does not feed its own plant any more, but serves 

 merely as a feeding- tube of the parasite, through which the building 

 materials which it requires are drawn from the host. 



When the stem of the parasite, which creeps horizontally in the 

 ground, has become sufficiently large and gorged with food materials, 



