

508 BOTANICAL GAZETTE ' ' [june 



or of pollen tubes within the nucellar tissue. Jager also speaks of 

 a ring-formed thickening at the outer end of the micropyle, a 

 feature not present in T. canadensis. 



• In its later development increase in thickness occurs below the 

 tip region, while growth in length is largely the result of chalazal 

 activity. In cross-section the young ovule is practically circular 

 in outline, but as it develops it becomes more elliptical, and, espe- 

 cially in the upper portions, pronouncedly 2-ridged, the ridges 

 corresponding with the lips. Frequently there are three ridges, 



remaining 



stant. 



finding very 



integuments. These ridges have been regarded as the midribs 



shown 



indicate 



yll character of the integument 

 histology of the integument ha 



for T. baccata by both Strasburger (35) and Bertrand (3), a 

 description which will also hold for T. canadensis. Before the 

 hardening of the seed coat the following regions (fig. 68) are to 

 be recognized: (1) the outer epidermis of large papillate cells, 

 covered with a very heavy cuticle; (2) the hypoderm, large thick- 

 walled cells, which become filled with brownish-red contents and 

 give color to the seed coat; (3) a sub-hypodermal layer of small 

 radially elongated cells; (4) a thick tissue of small irregular cells, 

 extending to the inner epidermis, next to which the cells are 

 longitudinally elongated; and (5) the inner epidermis, which in 



micropvle region forms 



consistin 



cells containing a dark staining material. Below the union of 

 the nucellus and integument the boundary between the two is not 

 distinct. Large secretory cells are abundant in the inner tissue, 

 and along the 2-keeled sides the strands of vascular elements 

 traverse the integument. Formation of the stony character of the 

 seed coat begins at the apex and extends downward, involving all 

 the tissue of the integument excepting the epidermis and hypoderm, 

 the cells becoming " stony," with very thick walls pierced by proto- 

 plasmic connections (fig. 69). The hardening begins very soon 



