234 INTRODUCTION TO PLANT GEOGRAPHY [CHAP. 



Common Pea needs plentiful moisture but thrives in cool regions, 

 whereas the Chick Pea is well adapted to dry conditions. Another 

 widespread and important crop plant of this general affinity is the 

 Lentil {Lens esciilenta), which has been cultivated since Neolithic 

 times and is thought to have originated in southwestern Asia. 



Mustards are extensively cultivated for their oil and use as greens 

 in Asia, as are the related Cabbages and Kales and their allies 

 [Brassica oleracea) in Europe and elsewhere for human and domestic 

 animal consumption (though originally for their oily seeds). The 

 Cabbages, etc., were evidently developed far back in antiquity from 

 a variable Mediterranean species exhibiting numerous local races ; 

 now they are grown practically around the world, occupying a wide 

 variety of soils and climates ranging from the low-Arctic to the sub- 

 tropics. Fig. 70, B, shows a fine bed of young Kale growing in 

 southern Greenland, with, behind, tall Rhubarb. 



Finally we should mention a few ' fruit vegetables ' such as the 

 Squashes and Cucumbers and their allies, many of which have been 

 extensively cultivated from early times, and the widely important 

 Tomato {Lycopersicum esciilentum), which springs from a group of 

 small-berried weedy natives of Peru. Most of these types do best 

 in warm and moist regions, to Vv'hich some are practically confined. 



(4) Forage Plants — While several of the above-mentioned crops 

 may be used in part for forage, there are some more specific forage 

 plants to be mentioned primarily in this connection. Foremost 

 among these are various Grasses, of which the Bluegrass or Meadow- 

 grass (Poa pratensis s.l.) is an outstanding example. Cytotaxonomi- 

 cally it is one of the most complex mixtures of polyploid hyhnds-cum- 

 apomicts known, appearing in numerous forms whose origin is often 

 obscure. Geographically it is widespread, particularly in the cooler 

 regions of the world. Ecologically it is unexacting and aggressive, 

 frequently forming a major constituent of pastures whether or not 

 it has been sown. Another important and widely cultivated forage 

 plant is Alfalfa or Lucerne {Medicago sativa), which was probably 

 the earliest forage crop to be developed — apparently in southwestern 

 Asia. Alfalfa prefers a deep, well-drained soil but is grown under 

 a wide range of moisture as well as temperature conditions. It 

 belongs to the Pea family as do also the Clovers and Vetches, which 

 are themselves of considerable significance in pasturage and hay. 



(5) Fibre and Oil Plants — In this extensive category the Cottons 

 (various species of Gossypium), Flax {Liniitn tisitatissimum), Hemp 

 (Cannabis sativa), Jute (species of Corchorus), and Peanut or Ground- 



