78 PeridiniedB 



Thus, the Prorocentracese may be quite as primitive as the Gymnodiniacese, 

 and not degenerate, reduced forms of the Peridiniacese as suggested by some 

 authors. 



NATURE AND AFFINITIES OF THE PERIDINIEA:. The question may be 

 asked why the Peridiniese (or Dinoflagellata) should be included in a 

 botanical text-book, and the answer would be that the balance of evidence 

 indicates that in the evolution of these organisms from more primitive 

 Flagellates the vegetable tendencies have so far become dominant that 

 over 90 per cent, of them are true vegetable organisms with a holophytic 



nutrition. 



The immense advance in the knowledge of the biology of unicellular 

 organisms during the past twenty years has shown that in many cases there 

 are no real distinctions between the animal and vegetable unicell. There 

 can be no doubt in the mind of any biologist who has made a special study 

 of the Flagellata, that this group of primitive organisms, exhibiting as it 

 does such great diversity in morphological and cytological structure, has 

 played a leading part in the commencement of various evolutionary series, 

 in some of which strong vegetable tendencies have become dominant, whereas 

 in others animal tendencies have come to the front. The more primitive 

 coloured Flagellates must be regarded as fundamentally vegetable organisms 

 with certain animal potentialities, and in groups of organisms which have 

 evolved from them the subsequent development of the animal tendency and 

 inhibition of the vegetable tendency may have been largely a question of 

 environment. 



The only sound basis for the discrimination between animal and vegetable 

 organisms is nutrition. It must be borne in mind that all protoplasts, be 

 they animal or vegetable, require practically the same classes of food-substances, 

 and, moreover, they assimilate them in precisely the same way. The vege- 

 table protoplast has, however, acquired the power of constructing its own 

 organic food-substances. In contrast, therefore, to the animal protoplast, 

 which requires its organic food presented to it in an available and assimilable 

 form, the vegetable protoplast is capable of performing the preliminary 

 synthetic work of constructing complex food-substances from raw materials. 

 This constructive work is carried out in the normal plant by means of chro- 

 matophores, and is dependent upon light, and hence the photosynthetic 

 activity of the typical vegetable organism is its fundamental characteristic. 

 The raw materials enter the protoplast in a state of solution, and the 

 elaborated materials which are the final products of photosynthetic activity 

 are from the beginning within the protoplast ready for immediate assimilation 

 whenever the action of enzymes renders them thus available. Such nutrition 

 is holophytic. 



