CHAPTER XVIII. 



EAR-COCKLE, PURPLES OR PEPPERCORN IN WHEAT, 

 OATS, AND RYE. 



Tylenchus tritici, Bast. 



FOR a clear comprehension of the disease of wheat, oats, 

 and rye, named ear-cockle, purples, or peppercorn, it is 

 necessary that the nature of an ear of wheat should be 

 well understood. We will therefore briefly describe the 

 structure of the inflorescence of wheat, so that the pecu- 

 liarities of ear-cockle may be made clear. 



An ear of wheat .is technically termed a spike, and 

 the spike consists of a rachis (literally a backbone) or zig- 

 zag stem, on which are placed numerous little clusters of 

 grains with their chaffy scales. Each cluster is termed a 

 spikelet, and as a single cluster or spikelet taken from 

 any part of a spike is generally the same in arrangement 

 as all the other clusters on the spike, we will remove one 

 cluster or spikelet for careful observation. 



At Fig. 40 is illustrated a spikelet of wheat enlarged 

 two diameters. It will be seen that the whole growth is 

 enclosed between two outer sheaths or bractlike scales, seen 

 at AA ; these are termed the two outer glumes glume 

 merely meaning " chaff." In wheat it is common to see 

 the two outer glumes enclosing five other growths. One 

 of these is an aborted growth seen at B, and the two 

 clusters on each side at C, D, E and F, each include two 

 bractlike scales, one a flowering glume, and the other 

 a pale. Each of the two inner growths encloses a pistil, 

 three stamens, and two minute scales. The lowermost and 

 outer bract of these two is termed the flowering glume ; 



