I Vol. 2 



182 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



ledony to monocotyledony ; and this fact strongly supports 

 the view that grasses are a comparatively primitive assem- 

 blage of monocotyledons. 



It is not difficult to explain the prolonged misconception 

 concerning monocotyledony. When the first detailed studies 

 of monocotyledonous embryogeny were made by Hanstein, 

 and supplemented by Famintzin, a form (Alisma) with a fila- 

 mentous proembryo was selected. If a form with a massive 

 proembryo had been selected for these early investigations, 

 there would probably have been no misconception, for in such 

 proembryos the peripheral (that is, lateral) cotyledonary zone 

 is so evident that it could hardly have escaped recognition. 

 Since that time, embryogeny that starts with a filamentous 

 proembryo has been regarded as the typical embryogeny, and 

 all other kinds of proembryos have been dismissed as excep- 

 tions. In the case of this filamentous proembryo, it was ob- 

 served that the terminal cell passed into the quadrant and 

 octant stages, and later a terminal cotyledon appeared. It 

 seemed safe to conclude that the terminal cell had developed 

 the terminal cotyledon. The inference was true so far as it 

 went, but it failed to recognize the fact that the terminal cell 

 develops other structures as well. With the origin of the 

 terminal cotyledon disposed of, the conclusion was confirmed 

 by the appearance at its base of a notch, from which arose 

 the stem tip. What could be more obvious than that the stem 

 tip is lateral in origin, and therefore must arise from the cell 

 of the proembryo behind the terminal one? In this way the 

 conventional embryogeny of monocotyledons was established, 

 and the relation of monocotyledony to dicotyledony became 



completely obscured. 



The facts not observed in these earlier investigations are 

 as follows : The terminal cell of the proembryo forms a group 

 of cells; the peripheral cells of this group develop the cotyle- 

 donary ring or sheath, on which two growing points appear. 

 One of these growing points soon ceases to be active, and 

 the whole zone develops in connection with the other growing 

 point; but at the base of the growing cotyledon a notch is 

 left by the checking of the other growing point. This notch 



