12 



ILLINOIS STATE GEOLOGICAL SURVEY 



Different plants produce spores of differ- 

 ent sizes and shapes and, as plants evolved 

 through time, the size, shape, and orna- 

 mentation of the spores changed, although 

 possibly not at the same rate as other ob- 

 servable changes in the plants. Because of 

 the great variety of spore types, their grad- 

 ual change in appearance through geologic 

 time, and the resistant nature of the spore 

 coat, the spore assemblages found in any 

 one sediment are likely to be different in 

 composition from those found in older or 

 younger beds. 



Also, because of possible geographic dif- 

 ferences in the distribution of plants, the 

 assemblages from the same bed may have a 

 slightly different aspect from one area to 

 another. Spores, especially microspores and 

 isospores, are produced in great numbers, 

 are small, and are widely dispersed by nat- 

 ural agencies such as wind and water cur- 

 rents. Although megaspores are generally 

 larger, sometimes very large, and are pro- 

 duced by only a segment of the floral popu- 

 lation — the heterosporous plants — they, 

 too, are sometimes widely dispersed. How- 

 ever, their distribution is more likely to be 

 restricted to an area close to their site of 

 production. 



Because we have very little chance of de- 

 termining whether a fossil spore performed 

 a male or female function in the life cycle, 

 unless cone studies have provided the 

 knowledge, an arbitrary lower size limit of 

 200 fx has been given for megaspores (Guen- 

 nel, 1952). Dijkstra (1946, p. 21) also re- 

 views the size problem. The size limit sug- 

 gested follows from using the Tyler sieve, 

 with a mesh opening of about 210 p, to sep- 

 arate the fine from the coarse residue. 

 Guennel further proposes the use of the 

 term "miospore" for all spores or sporelike 

 bodies less than 200 /x in size. These could 

 include isospores, microspores, small mega- 

 spores, pollen, and prepollen. 



The spores of Spencerisporites are iso- 

 lated spores similar to those occurring in 

 some of the cones of Spencerites, reported 

 as eligulate and homosporous. Thus, on 

 available evidence, the spores referred to 

 Spencerisporites would be considered iso- 



spores. Renisporites spores, rather small in 

 comparison with most megaspores, may be 

 megaspores, isospores, or microspores. 

 Monoletes and Parasporites are considered 

 prepollen. However, most of the spores 

 described here are megaspores of the ar- 

 borescent and herbaceous lycopsids and 

 lepidocarps. 



The larger spores show considerable dif- 

 ferences in size. In Cystosporites three mem- 

 bers of the original tetrad are abortive, 

 much smaller than the fertile specimens, 

 and sometimes much different in aspect. 



I - Tetrahedral 

 Tetrad 



2- Tetragonal 

 Tetrad 



Text fig. 1 (above). — Orientation of radially sym- 

 metrical spores. 



a. Spores in tetrad association. 



b. Proximal view of a single spore showing tri- 

 lete suture and contact areas. 



c. Lateral view of single spore. 



Text fig. 2 (below). — Orientation of bilaterally 

 symmetrical spores. 



a. Spores in tetrad association. 



b. Proximal view of single spore showing mono- 

 lete suture and contact areas. 



c. Transverse lateral view of single spore. 



