SPORE DEVELOPMENT AM) MORPHOLOGY 



13 



Spores are characteristically either radi- 

 ally (trilete suture, text fig. 1) or bilaterally 

 (monolete suture, text fig. 2) symmetrical, 

 the type of symmetry being controlled by 

 the division of the spore mother cell. For 

 descriptive purposes, spores are oriented 

 with reference to their original position in 

 the tetrad grouping (text figs. 1, 2; pi. 9, 

 fig. 3). The side of a spore toward, and in- 

 cluding, the original areas of mutual con- 

 tact in the tetrad is designated as proximal 

 (side, surface, or hemisphere). The side of 

 the spore external to, or away from, the cen- 

 ter of the tetrad is distal. The axis of a 

 radially symmetrical spore passes through 

 the center of the original tetrad. 



The apices of the four spores at the proxi- 

 mal poles originally touched in the tetrad. 



Bilaterally symmetrical spores have one 

 axis of symmetry through the long dimen- 

 sion of the spore and another through the 

 proximal surface of the spore and the cen- 

 ter of the distal surface. The contact areas 

 are the two or three surfaces of mutual con- 

 tact in the original tetrad. 



The trilete suture (pi. 15, fig. 2), or line 

 of dehiscence, forms along three radiating 

 lines; the trilete ray refers to one extension 

 of the trilete suture or its expression as lips 

 or as a fold. The monolete suture forms 

 along a single line (pi. 15, fig. 5a). Some 

 spores may possess very insignificant lips 

 bordering the suture, others may have 

 straplike lips (pi. 9, fig. 4a), and still others 

 may have lips surmounted by an apical 

 prominence (pi. 3, fig. 13). 



Those features influenced by the contact 

 relationship of spores during growth in a 

 tetrad are designated as haptotypic by 

 Wodehouse (1935). The contact areas may 

 be bounded by arcuate ridges, flanges, or 

 ornamentation which may or may not ex- 

 tend over the entire distal surface. Distal 

 ornamentation, in reference to megaspores, 

 is not generally strictly limited to the distal 

 hemisphere, but extends distally from the 

 arcuate ridges or contact areas. Specifically 

 inherited characters, such as distal orna- 

 mentation, of which the type, shape, and 

 size is relatively constant for any one spe- 



cies, are designated as emphytic by Wode- 

 house (1935). 



Some spores (pi. 13, fig. 2; pi. 14, fig. 11) 

 possess bladders or membranous air sacs 

 which are attached to the spore coat. Still 

 others possess a wrinkled inner membrane 

 (pi. 9, fig. 8a, b; pi. 10, fig. 9), sometimes 

 variously ornamented, referred to as an en- 

 dosporal membrane by Schopf (1938) , the 

 mesosporium of Dijkstra (1946) and H^eg, 

 Bose, and Manum (1955). Original spore 

 shape may vary from sac-shaped, to spheri- 

 cal, to distinctly oblate. The shape is usu- 

 ally more or less distorted by compression, 

 the manner of compression being deter- 

 mined by both the original shape and the 

 presence and kind of ornamentation. Thus, 

 the compressional form is usually charac- 

 teristic of a species, although other species 

 may also show the same form. 



In descriptions of the Illinois megaspores 

 particular attention is given to differences 

 in ornamentation noted on the lageniculate 

 megaspores. This general type of mega- 

 spore, showing some morphological varia- 

 tions, is known from beds as old as upper- 

 most Devonian, through the Mississippian 

 and Pennsylvanian, and into the Permian. 

 Therefore, any slight variation in ornamen- 

 tation may be helpful in differentiating 

 these megaspores. In contrast, those apicu- 

 late and smooth aphanozonate megaspores, 

 Triletes mamillarius Bartlett (sensu Dijk- 

 stra) and T. glabratus Zerndt (sensu Dijk- 

 stra), and the spores of T. triangulatus 

 Zerndt (sensu Dijkstra) are the least em- 

 phasized as to possible distinctions based on 

 ornamentation because of practical limita- 

 tions to the investigation. 



In the smooth aphanozonate megaspores, 

 possible distinctions would have to be based 

 on thickness of spore coat, length of rays 

 relative to spore diameter, or on the size 

 ranges of the spore diameter. The actual 

 size of a spore, or the range of a group of 

 spores, may mean little relative to its botan- 

 ical alliance. Bochenski (1936) illustrates 

 the wide range in spore size in cones of 

 Sigillariostrobus Czarnockii (400 to 2700//. 

 in one cone and 450 to 2900 ^ in another) . 



