THE CARPEL 203 



associated with wind pollination. A well-differentiated stigma — in con- 

 trast with the stigmatic crest — and a sealed carpel have been called 

 characters associated with insect pollination. The commissural stigma 

 is discussed later in this chapter. 



The Stylar Canal. The stylar canal is a space enclosed by the uniting 

 margins of a carpel — in syncarpous gynoecia, of all the carpels. It is 

 usually closed for part or all of its length by ti-ansmitting tissue. In 

 highly specialized syncarpous pistils, it may be complexly branched; the 

 branches may extend as strips of transmitting tissue beyond the bases 

 of the styles along diverse courses to the placentae. The transmitting 

 bands may vary in color from the ovary wall and, in the dicotyledons, 

 may be somewhat collenchymatous and easily dissected from the ovary 

 walls. A hollow style is occasional — Viola, Campanula, Reseda, Liliiim, 

 Yucca, Enjthwnium, Butomaceae. Pollen grains have been found in the 

 open canal of Biitomopsis and HiUebrandia but have not been seen 

 germinating there. In syncarpous gynoecia, the term stylar canal is 

 often applied to the transmitting tissue of the style only. It has been 

 suggested that it be applied to all parts of the branched transmitting 

 system, but the distal parts may be surface areas; where there is com- 

 plex extension of the tissue, it could well be termed the stigmatic- 

 tissiie sijsicm. 



The Terms Stigma, Transmitting Tissue, Stigmatic Tissue, Stigmatic 

 Crest. The stigma has been variously defined: morphologically, as the 

 distal part of the carpel, modified in form in adaptation to pollen re- 

 ception; functionally, as the tissues of the carpel, external and internal, 

 concerned with receiving and transmitting the pollen tube. The trans- 

 mitting tissue within the style and ovary has been called the internal 

 stigma. Where carpel borders with papillose epidermal cells are ap- 

 pressed and sealed ontogenetically, the external hairs are lost, and the 

 internal hairs form an internal stigmatic line that extends downward 

 along the placental line and around the ovules. In the primitive carpels 

 of Etipotnatia, which are without style and with an external stigma of 

 a mere tuft of apical hairs, connation has resulted in the loss of the 

 stigmatic crest, except for tlie internal band of papillose cells (Fig, 

 72A). 



The genus Drimijs shows stages in the restriction of the stigmatic 

 area to the distal part of the carpel and the internal surface. In the 

 section Tasmannia, the carpel borders are only appressed, and closure 

 is by glandular hairs; in the section Wintera, the borders are sealed, 

 and the crest reduced to a distal area. If the terms transmitting tissue 

 and conducting tissue were discarded, all the tissues that nourish and 

 control pollen-grain germination and pollen-tube growth could well be 



