Nov. 19, I92X Ash Content of Awn, Rachis, and Palea 449 



a high water content. The tissues arising from the fertiUzed egg cell 

 occupy a very small part of the growing kernel for several days after 

 fertilization. The ovary wall increases very rapidly. A tissue develops 

 at the end of the kernel arising from the ovary walls which persists for a 

 considerable time and which grows very rapidly for the first few days 

 after flowering. Histological sections of this tissue indicate that very 

 little is concerned in its growth except the addition of cell walls, the 

 enlarging of cells, and the increase of the watery cell content. A small 

 starch deposit is found in the cells, but it is negligible. This high pro- 

 portion of watery tissue might result in the drop of ash content immedi- 

 ately following fertilization. The gradual increase from then to maturity 

 may be due to the fact that the proteids contain a greater percentage of 

 ash than does the cell sap, or it may come about from a light deposit in 

 some limited tissue of the caryopsis. 



SUMMARY 



The awn of barley receives a very large deposit of ash, comprising over 

 30 per cent of the dry weight in some varieties. Barleys differ in the 

 amount of ash deposited in the awn and probably in the selective func- 

 tion of the absorbing roots. Within a variety the amount of ash in the 

 awn is correlated with the supply of soil water and probably with the 

 amount of water transpired. 



There are varietal differences in the amount of ash deposited in the 

 rachis. The rachises of hooded and awnless varieties are usually high in 

 ash and usually brittle. The tendency to shatter may possibly be over- 

 come in hooded varieties by crossing them with barleys of the Coast 

 type, which have little ash in their rachises. 



No part of the kernel proper is used as a repository for ash. The ash 

 of the kernel is the ash of cell sap and of highly active protoplasm. 

 When computed on the basis of the wet weight, the wet weight being a 

 measure of the organ when active, there is almost no variation in the 

 proportion of ash. During most of the period of growth the variation 

 is only 0.3 of i per cent, the content increasing gradually from slightly 

 less than 1 per cent in early growth to slightly more than i per cent at 

 maturity. 



