On Spores in the Carhoniferous Formation of Scotland. 91 



Zeiller examined, as transparent objects, some of these 

 bodies from his Sigillarian cones, and came to the conclusion 

 that they were single cells, or, in other words, spores, and 

 not sporangia. But, independently of this microscopical 

 evidence in favour of the sporal nature of these fossils, there 

 is the further evidence of their having been found in situ 

 in sporangia, as figured by Binney, Williamson, and others. 



In Selaginella the spore wall also most commonly consists 

 of two parts — the endosporium and exosporium. According to 

 Hoffmeister, both layers take part in the composition of the 

 long spines which adorn the outer surface of the macrospores 

 of some species. These spines on quite ripe spores appear 

 considerably shorter than when the spores are half-developed, 

 as the pressure which the rapidly-growing spores exert upon 

 one another breaks off the point of the spines.^ 



In recent Lycopods the spores are usually developed in 

 groups of four ; the macrospores of Selaginella affording good 

 examples of this. 



When examining the fossil macrospores in connection with 

 this paper, we have frequently found them occurring still 

 united in groups of fours {see PL IV., Figs. 16<i, 16e), and in a 

 few cases have found the four macrospores still contained 

 within a sporangium, which has been removed from its bract. 



The recent macrospores develop a small prothallus, which 

 is exposed at maturity by their bursting along the three con- 

 verging ridges ; and we have found some of the fossil macro- 

 spores split in a similar manner, suggesting that the pro- 

 thallus of these individuals had arrived at a certain state of 

 development before fossilisation took place. Some such 

 specimens are figured on PL III., Figs. 6<x, 7a. 



The fossil macrospores vary in external colour from black to 

 fawn, the latter colour depending on the extent to which they 

 have been weathered. The blackness of the spores appears, 

 however, to be usually the result of staining ; for the spores, 

 when broken or ground for microscopical examination, always 

 exhibit a brown or amber-coloured cell wall. This is especi- 

 ally observable when sections of spore coal are examined. 



1 Hoffmeister, On tlie Germination, Development, and Fructification of the 

 Higher Cryptogamia, translated by Fred. Currey, 1872, p. 388. 



