Floristik, Geographie, Systematik etc. 127 



das auffallend grosse Klimandrium fast röhrenförmig, oben am 

 Rande abgestützt, hinten zu beiden Seiten der Anthere in je ein 

 aufrechtes häutiges Läppchen ausgezogen. Stigma schmal, quer auf 

 der Säulenvorderseite unter dem hohen breiten Rosiellum liegend. 

 Hieher gehören: Alt. fimbriata H. B. et Kth. 1815, ^, t;/>^sc^ws Lindl. 

 1845 (= Prescottia crassicaiilis L. et Krzl. 1899, A. sceptmm Rchb. 

 1854 [alle drei aus Ekuador], A. marginata Rchb. 1878 [Peru], 

 A. boliviensis Rlfe 1895 [Bolivia]. 



III. Aa Rchb. f. 1854. Stengel erst nach Verwelken der Grund- 

 blätter erscheinend, mit dünnen Brakteen und Hochblättern besetzt. 

 Blüten sehr klein, äussere Perigonsegmente dünn, kahl oder fast 

 kahl; Labellum am Grunde mit 2 kleinen runden Schwielen verse- 

 hen, fast helmartig zusammengezogen; Perigonsegmente fast stets 

 kahl; Säule ebenso, stark verkürzt. Klimandrium kurz häutig be- 

 randet, meist stark reduziert. Rostellum stets sehr kurz, Stigma 

 gross, breit. Synonym mit Aa ist Myrosmodes Rcbh. fil. Hieher ge- 

 hören: Aa paleacea (H. B. et Kth.) Rchb. f , argyrolepis Rchb. f., mi- 

 bigena (Rchb. f.) Schltr., gymnandra, rostrata, paludosa, Mandonii, 

 calceata, inaeqiialis, Matthewsii, Weddeliana erosa (alle mit der Be- 

 zeichnung [Rchb. fil.] Schltr.), Hieronymi (Cogn.) Schltr., nervosa 

 (Kzl.) Schltr., Fiebrigii Schltr. Diese 15 Arten leben teils in Ekua- 

 dor, Bolivia, Peru, teils in Argentinien. 



Matouschek (Wien). 



Stapledon, R. G., On the plant communities of farm land. 

 (Ann. Bot. XXX. p. 161-180. 1916.) 



The weed flora of certain districts has been studied in terms 

 of communities and not as isolated species. For Statistical purposes 

 the specific frequency was used on arable soil and occasionally on 

 grassland, the percentage frequency being more usually employed 

 In the latter case. The distribution of the Chief arable species in 

 Mid-Wales and the Cotswolds is fully tabulated, the frequencies 

 under roots, cereals and seeds being recorded separately . Comparisons 

 are drawn between the flora of the Cotswolds and Mid-Wales, and 

 these results are again compared with those recorded elsewhere 

 by other workers. in Norfolk, Bedfordshire etc. A useful 

 reference is given to the flora of "sour" soils other than sands, as 

 peat, non-calcareous cla}' and non-calcareous sticky loam came 

 under Observation. 



On arable land the weed communities are much influenced by 

 the nature of the soil, and change in soil within a restricted area 

 is associated with change in the type of the weed communities. 

 Altitude also plays its part, but the difference in the weed flora 

 at the higher levels from that on the same at lower levels is partly 

 attributed to negligent husbandry. The crop itself also affects the 

 weed Community, but this again is largely due to the dilTerent 

 kinds of cultivation accorded to the various crops. With good 

 farming few species are associated with root crops, but under 

 tavourable conditions some species grow more luxuriantly under 

 roots than under any other crop. With poor cultivation the distinction 

 between the weed communities under roots and cereals is much 

 less marked. 



Finally, the purity of the seeds sown has much influence upon 

 the nature of the weed flora, both in the immediate year of sowing 

 and subsequently. W E. Brenchley. 



