544 WEED FLORA OF IOWA 



with a small cavity. These reach their highest development between 

 cotyledons and caulicle. First row of cells of the embryo nearly 

 isodiametrie, filled with protein grains and oil. 



Tumbling Mustard (Sisymbrium altissimum L,). 



On the addition of water the cell wall of the outer seed coat 

 becomes mucilaginous. Outer epidermal layer covered with cuticle, 

 cells elongated, on the addition of water, walls become mucilaginous 

 and show stratification. Cell walls of second layer thick, light 

 brown, followed by endosperm of two layers of cells, first elongated, 

 thick-walled. Cells of embryo as in S. officinale. 



Hairy Hedge Mustard (Sisymbrium canescens Nutt.). 



The testa of the small brownish cells consists of an outer 

 epidermal layer with thick walls. These cell walls become mucil- 

 aginous on the addition of water. This is followed by a layer of 

 several rows of brownish cells and a compressed layer, the nucellus. 

 The cells of the outer row of the embryo are smaller than the 

 underlying cells. 



Common Winter Cress or Yellow Rocket (Barbarea vulgaris R. Br.) . 



First layer of outer seed coat not well developed, cells elongated 

 in the direction of the seed. Cuticle covers the epidermal cells. 

 On the addition of water a slight mucilaginous modification takes 

 place. Second layer with thick lateral walls and quite large cell 

 cavities, colored brown. Third layer of rather thick-walled 

 parenchyma cells also colored brown, followed by endosperm as is 

 usual in cruciferous seeds. 



False Flax (Camelma sativa (L.) Crantz.). 



Seed coats consisting of four layers. The outer epidermal cells 

 not much longer than wide, on the addition of water become 

 mucilaginous and well stratified. On the addition of chloral hydrate 

 stratification is more evident. The cell walls are differentiated 

 into several layers. The second layer is not always developed. 

 Cells of third layer with thick walls and brown pigment, followed 

 by a narrow layer of thick-walled brown cells. The first row of 

 cells of endosperm, rather thick-walled, filled with protein grains, 

 the other layers of unequal development, cells elongated, thick- 

 walled ; followed by cells of embryo ; these contain protein grains 

 and fat. 



