1957] 



ANATOMY OF GUAYANA MUTISIEAE 



445 



structure. Outer ektexine may be seen to contain extremely fine striae or cham- 

 bers which are often at the limit of visibility of the light microscope. Since the 

 finer structure of the exine in Mutisieae has been little studied to date, the 

 pattern described above has not been previously reported for this group, although 

 the drawings of Erdtman (1952) for Mutisia speciosa suggest it. 



Variations in the thickness of the exine layers may be seen within an indi- 

 vidual pollen grain, although the relative thickness of layers, as seen at an arbi- 

 trarily chosen plane of section, is a character of taxonomic importance. An ex- 

 ample of variation in thickness of exine layers within a single pollen grain is 

 seen for Stenopadus hauchamacari in figure 90. In this pollen grain, the ektexine 

 layers show a greater thickness at the poles of the grain. As a comparison of the 

 measurements in table 1 shows, this difference is found in a number of the genera 

 considered, here. The thickness of the exine may be approximately constant within 

 a grain, however, with differential prominences of each layer at various places in 

 the grain. In Stomatochaeta cylindrica (fig. 92 3, C), for example, the endexine 

 and outer ektexine are thicker, the inner ektexine thinner, at the poles than at the 

 equator. In Stomatochaeta condensata (fig. 92 D), the inner ektexine is so nar- 

 rowed at the poles that no sculpturing could be seen in that layer, although the 

 outer ektexine is quite conspicuous. 



Although differences in polar versus equatorial thickness are not present in 

 all species, a transverse furrow (fig. 90 D, E), caused by a thinning in the ende- 

 xine, was seen in all species. This furrow is adjacent to the germ pore and runs 

 at right angles to the colpa. The shape of this transverse furrow, as shown in 

 figure 90D, was relatively constant for all the taxa investigated. This structure 

 was found by Wodehouse (1929 a, b) in many of the Mutisieae he studied. 



The genera below are arranged in two main groups. Those of the first (Steno- 

 padus through Vf underlie hia) have actinomorphic flowers and belong to the sub- 

 tribe Gochnatinae. In the remaining genera, with the exception of Glossarion, the 

 corolla form is exclusively bilabiate (Gerberinae). In Glossarion the corollas are 

 ligulate in form. 



Stenopadus. 



With the exception of S. campestris, the species of Stenopadus, as exempli- 

 fied by S. chimantensis fig. 90 A, B), have the following characters in common. 

 The grains have an elliptic outline, this shape being described by Erdtman (1952) 

 as subprolate for those of narrower shape, or prolate sphaeroidal for those ap- 

 proaching more nearly a sphaeroidal form. The outer ektexine is virtually smooth 

 (psilate), the spinulose emergences being one micron or less high. Stenopadus 

 campestris (fig. 89 A, B) shows a sphaeroidal shape, with minute spines (spinu- 

 lose) somewhat larger than those in the other species. All species of Stenopadus 

 show a relatively thin exine, approximately 3 to 5 microns in thickness. 



Explanation of Figures 89-91 



FIG. 89. Stenopadus campestris; A, pollen grain; B, optical section of grain at equator 

 (germ pores shown at right and left). FIG. 90. A, Stenopadus chimantensis, pollen grain; 

 B, S. chimantensis, optical section of grain at equator; C, S, huachamacari, optical 

 section of pole of grain; D, diagram showing portion of colpa of S. chimantensis, enlarged; 

 transverse furrow is shown above and below germ pore by dotted lines; E, portion of exine 

 in plane of optical section indicated by OS-OS in D. FIG. 91. A, Stifftia chrysantha, 

 pollen grain; S. chrysantha, optical section of grain at equator; C, Wunderlichia mirabilis 

 {Glaziou 2168G; GH), optical section of grain at equator. FIG. 90 D, E, X 1600; 91 A, B, 

 X 700; all others, approximately X 800. Specimens represented are indicated in table 1. 



