241 



has 34 vessels and a leptome group, while down both 

 sides there is a strand of sclerenchyma. 



The anatomy of the leaf has been described in the 

 closely related, perhaps identical species, Aristida pungens, by 

 DUVAL JOUVE (tab. 17, fig. 7) and TSCHIRCH (tab. 6, fig. 3). 

 The Transcaspian specimens examined by me agree in their 

 chief features with what has been found by these authors, yet it 

 seems to me that the single cell-layer of the green tissue has 

 a more pronounced palisade-form, and that the whole leaf 

 has larger internal air-cavities than in the figures cited. Some 

 figures of the structure of the leaf are given in fig. 64. The 

 leaf can roll up towards the inner (upper) surface which has 

 long hairs, and the epidermis includes hinge-cells. Like all 

 Paniceae, the plant has the veins surrounded by a starch- 

 sheath which is open on the leptome side in the larger 

 veins, while round the smaller ones it is interrupted on both 

 sides; this again is surrounded by a palisade layer. In my 

 specimens the lower surface is also furrowed, though faintly, 

 and in the furrows opposite the air-spaces amongst the 

 green tissue of the "prisms" there are stomata which are 

 slightly sunk; other parts of the epidermis are covered with 

 short, pointed hairs (fig. 64, J3, C). 



E. Therophytes. 



It has been repeatedly stated in previous pages that some 

 of the Therophytes are ephemeral spring-plants, while others 

 - the smaller number are summer-plants which persist 

 through the dry, warm summer. The following includes 

 observations on some of the species belonging to the latter 

 group. The ephemeral species might likewise repay a careful 

 investigation, for instance their variability as to xerophilous 

 structure, depending on the soil and time of development, 

 would be well worth examining. The material available 

 did not, however, permit of such an investigation, particularly 

 as regards anatomy. But the summer-plants seem to me 

 more interesting, and during the journey my attention was 

 chiefly directed towards them and towards collecting material 

 of them. 



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