HYDNORACEAE 177 



Plate 44. 



Hydnora africana Thunb. 



1. Thallus attached to root of Euphorbia mauritanica, with two buds and a fully 

 developed flower, the latter visited by a carrion beetle, Dermestes vulpinus. 2. Section 

 through thallus and the root of the host. 3. Flower at an early stage, long, section, one 

 perianth-lobe and part of androecium removed, bb. Bait-bodies with larva of Dermestes 

 feeding on one of them. a. Androecium. st. Stigma, pi. Placentae, o.c. Ovarial 

 cavity. 4. Transverse section through perianth-segment. 5. Part of fig. 4 enlarged. 

 6. Androecium. 7. A slice of the androecium with two pollen cells. 2/1. 8. Trans- 

 verse section through three pollen cells. 5/1. 9. Pollen grains (two views). 275/1. 

 10. Stigma. 11. Some placentae (pendulous), with numerous ovules. 3/1. 12. Lump 

 of seeds from fruit pulp. Nat. size. 13. Seed. 10/1. 14. Seed in long, section. 20/1. 

 em. Embryo. e. Endosperm, p. Perisperm, filled with starch. 15. Beetle found 

 feeding on bait-body in flower: Cryptochile costata (Fam. Tenebrioidae). 



Hydnora. 



The genus consists of eight species, three of which occur within our 

 limits, one, viz. Hydnora Solmsiana, having been recently described from 

 German South West Africa. 



Hydnora africana. This species grows principally on the roots of Euphorbia 

 mauritanica, sharing the wide distribution of this shrub in South Africa from 

 the Karoo of Worcester to the tropical parts of Great Namaqualand. It is, 

 however, not confined to this species of Euphorbia as its host, for we have 

 also observed it on Euphorbia decussata in the Karoo and on E. gummifera^ 

 E. gregaria and E. lignosa in the Namib and other parts of Great Namaqualand. 



The thallus or underground stem of the parasite is stout, 5- or 6-angled 

 and warty on the surface, spreading horizontally in the ground a few inches 

 below the surface. It does not produce any roots or rootlets, but when it 

 comes into contact with a root of the Euphorbia it sends strands of its tissue 

 into it, thereby causing an increased growth of the attacked root and finally 

 producing quite a large knob through which the parasite diverts the descending 

 sap of the Euphorbia into its own body. When sufficient material has 

 accumulated in the thallus it produces buds, which on increasing in size, finally 

 break through the surface of the ground and open just above it, the ovary 

 remaining underground. 



The whole plant is highly impregnated with tannin, and is therefore safe 

 from the attacks of herbivorous animals, but each perianth-lobe bears 

 a pure white, spongy body, which is free from tannin and at the same time 

 rich in albuminous matter*. This substance soon decays, producing the smell 

 of old meat, but even when quite fresh it acts as a bait for carrion beetles. 

 These, having once entered the flower, are prevented from leaving it by a 

 fringe of hairs and bristles on the margins of the perianth-lobes, and must 



* This organ was first described and figured by Robert Brown, being called by him 

 "pulvinulus carnosus." See Brown's beautifully illustrated essay "On the female flower 

 and fruit of Rafflesia Arnoldii and on Hydnora africana." Trans. Linn. Soc. 1844, P- 2 35- 

 Later authorities, however, appear to have overlooked Brown's statement, as these fleshy 

 bodies are not mentioned by them. 



M. 23 



