cook: seedling morphology 423 



cotyl is different, is not, however, a sufficient reason for sup- 

 posing that it is not the morphological equivalent of the other 

 internodes. To consider that an intern ode may be rhizophorous 

 along its entire length is only to recognize in the seedlings of 

 some of the grasses a condition that is common among palms, 

 and is retained through the entire life-history. To hold that a 

 root-bearing section of the axis above the scutellum is a part of 

 the cotyledon, seems a much more violent assumption than to 

 suppose that the internode of the coleoptile has retained the 

 primitive root-bearing function. To deny that the mesocotyl 

 represents the internode of the coleoptile is to assume that this 

 internode has been suppressed and a new organ intercalated in 

 its place. 



EPIBLASTS AS RUDIMENTARY PHYTOMERS 



Reduction or suppression of the leaf or of the axial element 

 of the phytomer being very common forms of specialization, 

 the epiblasts may be taken to indicate one or two rudimentary 

 internodes above the scutellum. Thus the mesocotyl would 

 belong to the third or fourth phytomer of the seedling, the one 

 that produces the first leaf sheath, the coleoptile. It is much 

 easier to believe that epiblasts represent rudiments of suppressed 

 phytomers than that they hark back to auricles of a formerly 

 more highly developed cotyledonary leaf. The so-called auricles 

 of grass leaves are so distinctly a part of the ligular specializa- 

 tion that their separate survival as epiblasts seems highly 

 improbable. 



A tendency of different organs to become more alike has often 

 to be recognized, but this idea of morphological convergence 

 would hardly justify the assignment of parts of a foliage leaf to 

 represent the scutellum, coleoptile, and epiblast. In order to 

 consider these organs as parts of the same leaf it has to be as- 

 sumed that the sheathing base, representing the most primitive 

 element of leaf structure, has been suppressed, while the blade, 

 ligule, and auricles have been retained. 



