Page Six 



EVOLUTION 



January, 1938 



Spores of Sporocarpon 



280 millions years old 

 magnified 100 times 



Codonotheca 



a pollen bearing organ 

 from Illinois 



The final discovery of the "missing-link" in 1903 veri- 

 fied a prediction made fully twenty years earlier. The 

 discovery of true seeds in actual connection with fern-like 

 foliage fulfilled the requirements for a perfect missing-link. 

 In 1883 the Austrian paleobotanist Stur noted that among 

 the abundant remains of fossil ferns of Carboniferous age, 

 there were many kinds for which no examples of fruiting 

 specimens had ever been observed. Surely these were not 

 ferns — even the more negative evidence of the absence of 

 fruiting examples needed consideration. For a time Stur's 

 question went unanswered, although in 1899 certain petri- 

 fied stems were recognized as having anatomical relation- 

 ships with both ferns and cycads. Upon these stems was 

 bestowed the name Cycadofilkes, or cycad-ferns. The 

 paleobotanist was getting close to an answer, but not yet 

 was he justified at anticipating a conclusion. 



It remained for Kidston and Scott in England and the 

 late David White in America to discover actual remains of 

 seed-bearing ferns which were immediately classed in a 

 new group — the Pteridospenns, or seed-ferns. We are 

 now supplied with sufficient data to know that the names 

 Pteridosperms and Cycadofilices refer to the same group 

 of plants. 



The pollen-bearing and seed-bearing structures of Illinois 

 Carboniferous seed-ferns immediately preceded the flower- 

 ing plants. Botanists generally consider them the remote 

 ancestral stock of all flowering plants. It is a tremendous 



Two Seeds of a Seed Fern 



A Nodule from the Carboniferous 

 200 millions years old 



gap between the Carboniferous seed-ferns which lived 200 

 million j'ears ago and the earliest recognized flowering 

 plants of 120 million years ago — plants which lived during 

 the Cretaceous age of dinosaurs. During the intervening 

 80 million years many profound changes took place with 

 numerous trials and errors toward the attainment of true 

 flowers. 



There are several so-called missing-links or transitional 

 types in the evolution of the flower which have as yet 

 escaped the scrutiny of the paleobotanist. Past experience 

 has taught us that much of the evidence is probably housed 

 in collections already preserved in museums but has simply 

 been overlooked. 



Only a century ago the study of fossil plants was in 

 its formative stages. Gradually a large number of facts, 

 substantiated by hundreds of important discoveries, has 

 accumulated, until we are in possession of the whole pic- 

 ture of the evolution of land plants. The study of paleo- 

 botany itself has evolved from the days when it merely 

 dealt with collections of natural curiosities. Today it has 

 taken its rightful place with the other fields of biological 

 thought. 



The upward course of plant evolution is an irrefutable 

 fact and the means by which this progress is measured is 

 nowhere better manifest than in the earliest Devonian 

 Psilophytales and in the seed-ferns. 



Is This Where Life Begins? 



From United States Department of Agriculture 



THE borderland between living organisms and chem- 

 ical substances is one of the frontiers of science in 

 which exploration is active. In this borderland exist the 

 viruses that cause a wide variety of diseases that aff^ect both 

 plants and animals, including man. Whether a virus lives 

 or is a chemical substance without life is a question that 

 puzzles both chemists and biologists. As exploration pro- 

 ceeds, the answer is coming more and more to depend 

 on a finely drawn definition as to what distinguishes living 

 from non-living substances. 



H. H. McKinney, research worker of the U. S. Depart- 

 ment of Agriculture, working with the virus of the com- 

 mon mosaic of tobacco, has developed evidence that the 

 virus has a very simple mechanism of inheritance. In the 

 past, scientists have usually regarded inheritance as a dis- 



tinguishing characteristic of living organisms. In popular 

 thought, reproduction or multiplication of a substance may 

 seem a convincing evidence of "life" but science knows 

 of many strictly chemical and non-living substances that 

 increase in a manner which is strongly suggestive of the 

 reproduction in organisms. 



Mr. McKinney has developed evidence that the virus 

 of common mosaic of tobacco mutates, giving rise to new 

 viruses which induce mosaic symptoms quite different from 

 common mosaic. Certain of the many virus characteristics 

 mutate more frequently than others. Some of the new 

 virus forms, or mutants, also mutate or give rise to still 

 other new viruses or sub-mutants. Of the many virus 

 characteristics of the common-mosaic virus some are re- 

 tained by its mutants and sub-mutants. Some of the char- 



