344 CALIFORNIA ACADEMY OF SCIENCES. [ProC. 3D Ser. 



in which the wall is to be at right angles to the long axis of 

 the proembryo. The section was cut not exactly in the 

 median plane, and the figure shows what appears to be a 

 large vacuole near the point of attachment of the embryo. 

 Examinations of the neighboring section show that this is 

 not a vacuole, the only visible vacuole present being in the 

 neighborhood of the dividing nucleus. When the first wall 

 is formed, however, vacuoles occur in both cells, and as the 

 further history of the embryo is traced, the greatest number 

 of these are to be found at and near its base. 



The second division of the embryo occurs in the basal 

 cell, so that the cell-walls of the pro-embryo are formed in 

 basipetal succession. Norner separates the grass embryos 

 into three groups based on the direction taken by the first 

 two walls. His "Type I" may be represented by figure 

 31, in which the first wall is at right angles to the long axis 

 of the embryo, and the second parallel to it. Figure 32 

 represents " Type II " of Norner in which the first wall is 

 at right angles to the long axis of the embryo, but the 

 second wall cuts this at an acute angle. Such embryos as 

 that shown in figure 30 fall under "Type III". In this 

 embryo the first wall is at an acute angle with the long axis 

 of the embryo, and the second strikes the first at a sharp 

 angle. As the figures indicate, the three types given by 

 Norner for all grasses studied by him are present in Avena 

 fatna. Of these types the first is perhaps the most common; 

 when the others are met in old embryos, the cell formation 

 is so confusing that it practically defies solution. 



The third cell-wall is formed in the distal cell of the pro- 

 embryo, bisecting it parallel to the long axis of the pro- 

 embryo, and is the first cell division belonging to the embryo 

 proper (fig. 30). The fourth division is a transverse wall 

 formed in the basal proembryo cell and cuts off the sus- 

 pensor. No subsequent division was observed in the 

 suspensor cell. At this stage in the development of the 

 embryo there are four segments and five cells. There are 

 two distal cells in the first segment, and between them and 

 the suspensor two superimposed cells, of which the second 

 belonged to the proembryo, and the third was derived from 



