THE FACTORS OF ORGANIC F VOLUTION. 61 



we say of organic masses, characterized by such extreme chemical in- 

 stability ? instability so great that their essential material is named 

 protein, to indicate the readiness with which it passes from one isom- 

 eric form to another. Clearly the necessary inference is that this effect 

 of the medium must be wrought inevitably and promptly, wherever 

 the relation of outer and inner has become settled : a qualification for 

 which the need will be seen hereafter. 



Beginning with the earliest and most minute kinds of living things, 

 we necessarily encounter difficulties in getting direct evidence ; since, 

 of the countless species now existing, all have been subject during 

 millions upon millions of years to the evolutionary process, and have 

 had their primary traits complicated and obscured by these endless 

 secondary traits which the natural selection of favourable variations 

 has produced. Among protophytes it needs but to think of the multi- 

 tudinous varieties of diatoms and desmids, with their elaborately-con- 

 structed coverings ; or of the definite methods of growth and multi- 

 plication among such simple Algce as the Conjugates y 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 con- 

 templating the totality of the facts. 



The first cardinal fact is that all protophytes are cellular all show 

 us this contrast between outside and inside. Supposing the multitudi- 

 nous 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, indi- 

 cate, 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 primitive units, Sachs * says of the lowest Algae that " the con- 

 jugated protoplasmic body clothes itself with a cell- wall" (p. 10) ; 

 that in " the spores of Mosses and Vascular Cryptogams " and in " the 

 pollen of Phanerogams " . . . " the protoplasmic body of the mother- 

 cell breaks up into four lumps, which quickly round themselves off and 

 contract and become enveloped by a cell-membrane only after com- 

 plete separation" (p. 13) ; that in the Equisetacece "the young spores, 



* Text-Book of Botany, dtc. by Julius Sachs. Translated by A. W. Bennett and "W. T. 

 T. Dyer. 



