LIFE IN PRIMARY PERIOD 201 



Inostranzeff has given them the name of shungite. They may 

 result from vegetable fossils more highly altered than those 

 which formed coal measures. 



During the Silurian Period Algae of the Siphoneae family 

 at last appear, and others that recall the large Laminaria of 

 to-day. With these are associated remains that would seem 

 already to be divided up into the three classes of vascular 

 Cryptogams : Horse-tails (Annularia) , Ferns (Sphenophyllum) , 

 and Club-mosses (Sigillaria). The presence of Siphoneae is of 

 especial interest. These Algae, which still exist, may grow to 

 a large size, remain spheroidal (Codiaceae, such as Grivanella), 

 or branch out like the higher plants, the branches recalling 

 leaves and even forming whorls (Dasycladeacae, Palceoporella, 

 Rhabdoporella, Vermiporella). Despite this, they do not show 

 the cellular structure so general in organisms that are no longer 

 microscopic. The body, enclosed within a wall of cellulose, 

 supported by an irregular network of threads of the same 

 substance, consists only of an amorphous protoplasmic mass 

 within which are scattered numerous nuclei. In view of this 

 we may ask whether the cellular structure of almost all the 

 present animals and plants is not a secondary development, 

 resulting from an equal distribution of an originally continuous 

 protoplasmic mass between the nuclei which contain the sub- 

 stances regulating nutrition, such as chromatin. In the 

 cellular Algae we pass, by finely graduated transitions, from 

 organisms reduced to a minute sphere (Prutococcus) , or to a 

 single cell (Desmidiaceae, Diatomaceae) to filamentous Algae 

 (Confervae), Algae spread out in undivided lamellae (Ulva), 

 dentated or serrated (Fucus), and others in which we can 

 already discern a pediculate portion simulating a root, and a 

 free, more or less cylindrical part analogous to a leaf-bearing 

 stem (Cystocira, Macrocystis, etc.). Rudimentary leaves 

 already begin to be characteristic of cellular terrestrial plants 

 of the class Muscineae, in which gradual differentiations can 

 be traced from Hepaticae, such as Riccia or Marchantia up to 

 Mosses. Thus, leaves which in the higher plants are so indi- 

 vidualized that we can say that such plants are really an 

 assemblage of leaves arising one from the other, whose con- 

 crescent parts have formed the branches and the stem (p. 100), 

 have only acquired this individuality, like the cells, as a 

 secondary development. Just as the intimate structure of 



