INTRODUCTION 



ON THE EXINE MORPHOLOGY OF THE SACCATE 

 POLLEN GRAINS IN RECENT GYMNOSPERMS 



The saccate pollen grains in recent gymnosperms are heteropolar, bi- 

 lateral or radiosymmetric (sometimes slightly asymmetric). They consist 

 of a body (corpus) and a varying number of airsacks or bladders (sacci). 

 The aperture is distal, and should often perhaps more appropriately be 

 referred to as a tenuitas (i.e., a thin aperturoid area functioning as an 

 aperture and gradually merging into the surrounding exine). It has earlier, 

 as a rule, been described as a sulcus or a sulcoid groove. 



The surface of the corpus of a pollen grain with n bladders can be divided 

 into the following areas: n saccale areas, forming the floor of the sacci, 

 n mesosaccale areas (mesosaccia), i.e. areas between the sacci and in the 

 same latitude as these, and finally two aposaccale areas (aposaccia), 

 one at the distal pole, and the other, usually much larger than the former, 

 in the proximal face of the grain with the proximal pole in its centre. 



With respect to the thickness of the exine of the corpus certain pollen 

 types (cf. e.g. Figs. 53 and 57) exhibit two distinct exine areas: a proxi- 

 mal, crassi-exinous (referred to as cap, cap pa), and a distal, tenui-exinous 

 (referred to as cappula). The non-saccale exine of the cappa consists of 

 comparatively thick sexine and thin nexine. The outer, ectosexinous part 

 of the sexine is usually thin, tegilloid, and as a rule connected to the 

 nexine— except within the sacci— by baculoid, densely spaced endo- 

 sexinous elements. 



The sacci are separated from the interior, non-exinous parts of the corpus, 

 by saccale nexine. Their outer wall consists of thin ectosexine which is 

 often perforated (shown in electron micrographs— not published — by Erdt- 

 man and Thorsson in 1950). The small holes (micropuncta) are usually 

 difficult to observe through an ordinary light microscope. In the majority 

 of the Tsiiga species the ectosexine of the sacci (as well as that of the corpus, 

 cf. Fig. 73) is studded with spinules or small spines. Attached to the inner 

 surface of the outer wall of the sacci are endo-sexinous elements protruding 

 into the lumen of the bladders (in Pherosphaera fitzgeraldii stray endo- 

 sexinous rods are also found on the saccale nexine). These elements are 

 more widely spaced than those of the body. Branched or unbranched, single 

 or combined in different ways, they tend to produce an array of patterns 



