I04 BOTANY OF CROP PLANTS 



stem, the hypocotyl, is between the primary root and the 

 growing point. In other words, the embryonic stem, or 

 hypocotyl, terminates at the anterior end in a growing point 

 and at the posterior end it is prolonged into the primary root. 

 There are several immature foliage leaves surrounding the 

 growing point and attached to the upper end of the hypo- 

 cotyl. The growing point and foliage leaves are surrounded 

 by a leaf sheath, the coleoptile or pileole. At the point where 

 the root sheath merges into hypocotyledonary tissue, there 

 is a small projection, the epihlast. Lying next to the endo- 

 sperm is a speciahzed structure, the scutellum, which is 

 attached to the hypocotyl. It has been suggested that the 

 scutellum and epiblast represent two cotyledons, one of 

 which (scutellum) is highly modified, the other (epiblast) 

 suppressed. 



We are all familiar with the seedlings of bean or squash. 

 In these, there are two cotyledons (seed leaves) which 

 are brought above ground and function for a while as 

 green leaves. Plants with two cotyledons are said to be 

 dicotyledonous. The scutellum of grasses is regarded as a 

 cotyledon, morphologically. Plants Hke grasses, sedges, 

 rushes, liUes, etc., which have one cotyledon are said to be 

 monocotyledonous. If the epiblast represents a rudimentary 

 second cotyledon, as its position on the embryo would seem 

 to indicate, it stands as evidence of the fact that monocoty- 

 ledonous plants had dicotyledonous ancestry. Rudimentary 

 structures are a great aid in tracing the racial history of all 

 organisms. 



The scutellum remains in the seed during germination, 

 serving in the absorption of and transfer of food from the 

 endosperm to the growing regions. The outermost layer 

 of the scutellum, where it adjoins the endosperm, is a 

 columnar epithelium. It is probably this layer which secretes 



