50 THE FACTORS OF ORGANIC EVOLUTION. 



now existing, all 1 a/&quot;e been subject during millions upon 

 millions of years to the Evolutionary process, and have had 

 their primary traits complicated and obscured by those 

 endless secondary traits which the natural selection of 

 favourable variations has produced. Among protophytes 

 it needs but to think of the multitudinous varieties of 

 diatoms and desmids, with their elaborately-constructed 

 coverings ; or of the definite methods of growth and 

 multiplication among such simple Algse as the Conjugate ; 

 to see that most of their distinctive characters are due to 

 inherited constitutions, which have been slowly moulded by 

 survival of the fittest to this or that mode of life. To 

 disentangle such parts of their developmental changes as 

 are due to the action of the medium, is therefore hardly 

 possible. We can hope only to get a general conception of 

 it by contemplating the totality of the facts. ^ 



The first cardinal fact is that all protophytes are cellular^J 

 all show us this contrast between outside and inside. 

 Supposing the multitudinous specialities of the envelope 

 in different orders and genera of protophytes to be set 

 against one another, and mutually cancelled, there remains 

 as a trait common to them an envelope unlike that which 

 it envelopes. The second cardinal fact is that this simple 

 trait is the earliest trait displayed in germs, or spores, 

 or other parts from which new individuals are to arise; 

 and that, consequently, this trait must be regarded as 

 having been primordial. For it is an established truth of 

 organic evolution that embryos show us, in general ways, 

 the forms of remote ancestors ; and that the first changes 

 undergone, indicate, more or less clearly, the first changes 

 which took place in the series of forms through which the 

 existing form has been reached. Describing, in successive 

 groups of plants, the early transformations of these primi 

 tive units, Sachs* says of the lowest Algss that &quot;the con- 



* Text-Book of Botany, d-c. by Julius Sachs. Translated by A. W. Bennett 

 and W. T. T. Dyer. 



