Chap. IX] 



DESERTS 



611 



immediate sandy neighbourhood of Port Said, and to the most northerly 

 part of the Algerian Sahara, near Biskra (Eig. 345), where I happened to be 

 for a short time during the spring rain, which appeared scarcely to moisten 

 the ground. The firm, usually loamy, soil of the desert tract between the 

 oases looked like a very meagrely planted and very peculiar garden, in 

 which the individual plants were separated from one another by bare patches, 

 one meter and more wide. Most of them were small, roundish, dense shrubs, 

 which, when observed superficially, resembled one another so much that it 

 came as a surprise to find, on looking at them closely, different kinds of 

 leaves or flowers (Leguminosae, Zygophyllaceae) ; there was, however, no 

 want of horizontally-spreading under-shrubs pressed close to the ground, nor 

 of rough, besom-like forms ; the 

 latter usually belonging to an 

 Artemisia, which was frequently 

 accompanied by a juicy, tall, 

 purple Orobanche. The sandy 

 soil of dry water-courses was 

 populated by tamarisks covered 

 with salt. These were the repre- 

 sentatives of the flora associated 

 with subterranean water. The 

 rain-flora consisted of much 

 smaller and more delicate plants ; 

 in particular the rosettes of 

 Scorzonera alexandrina, a nar- 

 row-leaved inconspicuous herb 

 with large violet fragrant stel- 

 late capitula on short peduncles, 

 showed themselves everywhere, 

 also Odontospermum pygmaeum 

 (Fig. 342) and the well-known 

 Anastatica hierochuntica ; the 

 latter, however, only in the dry 

 beds of the water-courses. 



Upon rain-herbs of this type in the desert one cannot directly observe 

 any trace of the unfavourable nature of the climate. This is revealed in- 

 deed in their very rapid development and the short duration of their life, 

 but neither in the delicate herbaceous stems and leaves, nor in their thin 

 roots, which, in contrast with those of plants associated with subterranean 

 water, penetrate the soil no deeper than the rain, nor in their flowers, 

 which are frequently of considerable size, is the climatic influence visible. 

 Volkens has investigated a great number of these desert annuals, and 

 in most cases could discover no xerophilous characteristics in such plants 



R r 2 



Fig. 342. Flora of the Sahara. Odontospermum 

 pygmaeum, O. Hofif. I. with closed capitula (dry) ; 

 2. an open capitulum (moist). Natural size. 



