May, 1922.] ON THE GERMINATION AND THE POLYEMBRYONY 



49 



only indicated in the earliest embryonic stage of development. The 

 anatomical features of these organs also afford striking confirmatory 

 evidence of the validity of this interpretation. It is especially note- 

 worthy, as shown by Schlickum, 29 that the vascular bundles found 

 in these organs indicate that we are dealing with structures that 

 show the exarch types of organization rather than the normal type 

 of epicotyledonar development. The behavior of the epiblast is quite 

 in keeping with this interpretation, as will be seen from Fig. 1. 



The epiblast may develop absorbing hairs from its apical cells or 

 from any of its cells ; and in fact it responds to enviromental factors 

 in the same manner as does the coleorhiza. In this connection, the 

 observation of Haberxandt on the remarkable resemblance of the 

 scutellar epithelial cells of Briza minor to root hairs is significant. 

 It would seem as though the entire development from the cotyledonary 

 plate partook of the haustorial root nature, (See Tschirch) 35 save in 

 the case of the coleoptile. This organ, perhaps owing to its mass 

 growth with the shoot and its consequent removal from the co- 

 tyledonar\ r region, would appear to have lost its haustorial function. 



The germination of the grains displays the usual features characte- 

 ristic of the grasses. The coleorhiza first emerges from the grain, 

 developing hairs at once. This growth is followed directly by the 

 extension of the coleoptile, and shortly afterwards the primary root 

 pierces the coleorhiza. The species under consideration develop, but 

 a single root in the embryonic stages, thus differing from many grasses, 

 as Arena, Triticum, Andropogon, etc. The secondary roots, usually 

 two in number originate from the first and second nodes of the stem, 

 and they appear almost simultaneously, and constitute the first 

 permanent roots of the plant. 



In the germination of the grains of Poa pratensis numerous 

 examples were studied where two embryos appeared. These embryos 

 were commonly placed side by side (Fig. 2), but in some instances 

 one of the embryos would occupy a rather oblique position to the 

 median plane of the grain. Each embryo was quite normal in 

 structure and developed in the manner outlined above. As a rule, 

 they were also of equal vigor and developed into normal plants. An 

 interesting case was observed where two shoots were inclosed in a 

 single coleoptile and there was but a single normal coleorhiza which 

 contained two roots, each associated with one of the shoots (Fig. 3). 



The most striking departure from the normal type of development 

 was found in Poa pratensis. In several instances the grains were 



