562 WEED FLORA OF IOWA 



Wild Carrot {Dcmcus carota L.)- 



The eremoearp consists of an outer epidermis of cells some- 

 what longer than broad; the underlying cells are of similar struc- 

 ture except the cells near the inner epidermis, which are much 

 longer than wide;, a large oil duct occurs in each rib. The testa 

 consists of a single layer of parenchyma cells and a few rows of 

 compressed elements, probably the nucellus. The endosperm of 

 thin-walled parenchyma cells contains protein. 



Cow Parsnip {Heracleum lanatum). 



An outer epidermis with outer walls thickened. The underlying 

 parenehjnna cells similar, followed by a layer of thick-walled 

 selerenchyma cells. The testa of single layer of ceUs. The en- 

 dosperm cells contain protein. 



ASCLEPIADACEAE, MILKWEED FAMILY. 



Milkweed (Asclepias syriaca L.). 



The flattened reddish brown seeds consist of an epidermis of 

 isodiametric cells; the outer walls wavy, and thickened; each cell 

 with a projecting point, outer walls colorless, contents brownish; 

 the epidermis is followed by 10-14 rows of thin-walled parenchyma 

 cells containing a brownish pigment This layer is followed by 



em 



Fio. 429. Microscopic structure of the seed of Milkweed (.Asclepias syriaca). 



ep=epldermls. p=parenohynia. n=nucellus. em=embryo. 



(Drawing by L. H. Pammel and Charlotte M. King.) 



