GENUS T RILE lis 



15 



were then taken again, unless, of course, the 

 specimen had cracked on drying. The maxi- 

 mum diameter oi each specimen, both wet 

 and dry, is well shown on the scatter dia- 

 grams that are given in text figure 3. The 

 shrinkage observed ranges from less than 10 

 percent to more than 35 percent and has a 

 pronounced effect on the means of the max- 

 imum diameters of the spores of the three 

 species. In contrast to this large amount of 

 shrinkage, some spores (T. mamillarius, 

 sensu Dijkstra) from a Casey ville age coal 

 (maceration 795) macerated in 1954 showed 

 a consistent 5 percent shrinkage. 



Probably many factors contribute to the 

 observed differences in size between wet and 

 dry specimens. The preservation of the 

 spores, the type of maceration method 

 used, the length of time specimens are 

 stored, and the kind of medium in which 

 they are stored, all may affect total size 

 when observed wet as opposed to the size 

 when observed dry. The differences in di- 

 mensions, if any, of a single specimen, trans- 

 ferred first from water to alcohol, then to 

 xylol, and then mounted in balsam have 

 not been checked as yet. 



That some shrinkage occurs, even when 

 freshly macerated specimens are dried, can- 

 not be denied. Extensive, laborious tests 

 would have to be run in order to determine 

 the effect of different maceration processes 

 and length of storage time on the observed 

 differences in size. It is possible that some 

 of the observed distinctions between spores 

 described by different authors, from differ- 

 ent coals or from different areas, may be 

 resolved as only the effect of differential 

 shrinkage rather than the result of any bo- 

 tanical distinctions in the plants producing 

 these spores. In any event, this is but one 

 facet to the study of fossil megaspores. The 

 actual expectable differences possible with- 

 in a cone or between cones of the same 

 plant will not be fully appreciated until 

 many more cone studies have been reported 

 upon. 



Probably the most expedient solution to 

 the problem is to gi\e measurements based 

 on either dry or balsam-mounted speci- 

 mens, indicating clearly which type is 



used. The descriptions of the spores of the 

 different species arc based on my observa- 

 tions of spores, principally from Illinois 

 coals, and not on previously published de- 

 scriptions unless otherwise indicated, so that 

 the descriptions and si/e measurements 

 may differ somewhat from previously pub- 

 lished ones. 



Nomenclature of fossil spores in this pa- 

 per is that determined by the International 

 Rules of Botanical Nomenclature. These 

 rules are adhered to by most authors in 

 order that the system of reference be under- 

 stood internationally, and are simple, pre- 

 cise, and, above all, stable. The genera re- 

 ferred to in the present paper are artificial 

 in that they are based on spores of plants, 

 in contrast to the criteria used to determine 

 genera of modern plants, and may corre- 

 spond generally to categories of familial, or 

 higher, rank. As research continues, espe- 

 cially that on fossil fructifications, these 

 artificial groupings will become restricted 

 to as small a natural category as is possible 

 with fossil plants. Individual interpreta- 

 tion of the magnitude of differences that 

 determine species or varieties within a gen- 

 eric group varies, as does the interpreta- 

 tion of genera based on fossil spores. In 

 time the nomenclature may express the 

 taxonomic position of the plants more 

 closely. 



DESCRIPTIONS OF MEGASPORES 

 AND "LARGE" SPORES 



Genus Triletes (Bennie and Kidston) 



ex Zerndt, 1930 



Type species: Triletes glabratus Zerndt, 



1930c 



Megaspores referred to Triletes are radi- 

 ally symmetrical, marked by a trilete suture 

 on their proximal surfaces. The extremities 

 of the trilete rays may be connected by arcu- 

 ate ridges. Elaborate processes may be de- 

 veloped at the outer edges of mutual con- 

 tact of the sister spores in the tetrad. Distal 

 sin laces are smooth to ornamented; proxi- 

 mal surfaces, if ornamented, are generally 

 ornamented to a lesser degree than are dis- 

 tal surfaces. Schopf (1938) pointed out that 



