74 ANCIENT PLANTS 



Among the plants of to-day there are many varieties 

 of the simple single-celled reproductive masses which 

 are called spores, and which are usually formed in large 

 numbers inside a spore case or sporangium. Among the 

 higher plants seeds are also known in endless variety, all 

 of which, compared with spores, are very complex, for 

 they are many-celled structures, consisting essentially of 

 an embryo or young plant enclosed in various protec- 

 tive coats. The distinction between the two is sharp 

 and well defined, and for the student of living plants 

 there exists no difficulty in separating and describing 

 seeds and spores. 



But when we look back through the past eras to 

 palaeozoic plants the subject is not so easy, and the two 

 main types of potentially reproductive masses are not 

 sharply distinct. The seed, as we know it among 

 recent plants, and as it is generally defined, had not 

 fully evolved; while the spores were of great variety 

 and had evolved in seyeral directions, some of which 

 seem to have been intermediate stages between simple 

 spores and true seeds. These seedlike spores served 

 to reproduce the plants of the period, but their type 

 has since died out and left but two main methods among 

 living plants, namely the essentially simple spores, the 

 very simplicity of whose organization gives them a secure 

 position, and the complex seeds with their infinite variety 

 of methods for protecting and scattering the young em- 

 bryos they contain. 



Among the CC)al Measure fossils we can pick up some 

 of the early stages in the evolution of the seed from the 

 spore, or at least we can examine intermediate stages 

 between them which give some idea of the possible 

 course of events. Hence, though the differences from 

 our modern reproductive structures are so noticeable a 

 feature of the palaeozoic ones, it will be seen that they 

 are really such differences as exist between the members 

 at the two ends of a series, not such as exist between 

 unrelated objects. 



