542 



WEED FLORA OF IOWA 



Fig. 418. Microscopic structure of some Cruciferous seeds iCraoiferae). 

 I. False Flax iCamelina sativa). II. Black Mustard (.Brassica nigra). III. 

 Common Mustard (B. arvense). TV. Winter Cress (.Barbarea vulgaris}, 

 V. Peppergrass (Lepidium virginicum) . VI. Tumbling Mustard (.Sisym- 

 brium altiaaimum) . VII. Shepherd's Purse (.Capsella bursa-pastoris) . 

 t=testa. p=parenchyma cells. n=nucellus. em=enibryo. 

 I, II, III, and IV. Elongated palisade cells below the epidermal layer and 

 parenchyma cells. To the right of I, epidermal cells after the addition 

 of water. 



(Drawings by L. H. Pammel.) 



this layer differ greatly with, reference to their size, being scarcely 

 at all developed in places, in others nearly as large as the cells 

 of the outer layer. 



