ii6 



BOTANY OF CROP PLANTS 



where cold or wet weather prevents flower opening. In 

 India, it has been observed that cross-pollination in wheat is 

 more frequent than in northern climates. 



In the wild wheat of Palestine, the kernels 

 are normally retained by the spikelet. It 

 differs also from domesticated wheat in the 

 order of maturity of the spikelets. In do- 

 mesticated wheat, the first spikelets to de- 

 velop flowers are those near the middle of 

 the head, while in the primitive wheat the 

 terminal spikelets are the first ones. Primi- 

 tive wheat also shows some indications of 

 sexual dimorphism. Some plants have been 

 observed to bear protogynous, others pro- 

 tandrous, flowers. The spikelets of this wild 

 form never mature more than two grains 

 (Fig. 41), and those of the same spikelet are 

 unequal in size. The smaller grain is borne 

 by the lower flower in the spikelet; this 

 flower has the longer awn too. 



A. Schulz thinks that many, but not all, of the primi- 

 tive wheat individuals found by Aaronsohn are hybrids 

 between T. agilopoides ihaoudar and dicoccoides. The 

 origin of the different types of cultivated wheats, as 

 given by Schulz, is shown in the following: 



1. Einkorn series, of which T. tegilopoides is the 

 prototype. 



2. Emmer series, of which T. dicoccoides is the stem 

 form. From this have come dicoccum, durum, turgidum, and polonicum. 



3. Spell series, of which the stem form is unknown. From this have come 

 spella, compactum, asliimm, and capUatumi 



Fig. 41. — Spike- 

 let of wild emmer 

 (Triticum dicoc- 

 cum dicoccoides) . 



Enviromnental Relations. — Wheat is grown under a wide 

 range of temperature conditions. Some varieties come to 

 maturity and yield well as far as 64° N. latitude in Norway, 



