TYPICAL FORMS OF PLANT KINGDOM 



97 



but its mere existence, however brief, authorizes us in classing 

 the organism as a plant. Certain organisms throughout their 

 whole lives may resemble either zoospores of Algae or Fungi, or 

 else myxomycetes, and differ only in the complete absence of 

 the formation of a cellulose membrane. It is these forms which 

 link up the vegetable and animal kingdoms. Here the 

 differentiation between the two is quite artificial, though it 

 is legitimate to consider these ambiguous forms — devoid as 

 they are of the positive characters that distinguish true plants — 

 as members of the animal kingdom ; the more so as the absence 

 of cellulose, a negative feature, goes with that mobility which 

 is a positive character of animal organisms. Because of that 

 very immobility imposed on their cells by this rigid membrane 

 of cellulose, the evolution of plants has been relatively simple. 

 When isolated, these cells appear in the form of rounded 

 granules, 1 rods, 2 spindles, 3 crescents, 4 spirals, 5 etc. They can 

 be juxtaposed so as to form chains, 6 networks, 7 small solid 

 cubes, 8 and fans supported on a stem, 9 or even spherical 

 masses capable of swimming 10 whenever the cells of which they 

 are built up are furnished, as in Volvox, with vibratile flagella. 

 Generally they are placed end to end so as to form those inter- 

 lacing green filaments called confervas, which abound in fresh 

 water. Analogous filaments, welded together in parallel lines 

 and giving rise to lateral branches, form the body or thallus of 

 Char a. Cells that are more or less polyhedral and dissimilar in 

 shape arranged in several layers, can build up laminated or 

 even massive structures of large dimensions such as those that 

 form the varecs of our coasts, the great marine Laminaria 

 many metres long, or those enormous floating Macrocystis 

 found in southern waters, which can spread out their branches 

 over more than a hundred metres. Plants thus formed entirely 

 of cells almost alike in structure and juxtaposed are subdivided 

 into two groups : Algae, when they are coloured green by 

 chlorophyll ; and Fungi, when, devoid of chlorophyll, they live 

 at the expense of other organisms — as animals, in their very 

 different way, are also compelled to do. 



In spite of their homogeneous structure, Algae may exhibit 



1 Micrococcus, Protococcus, etc. 



Naviculcc. 



Spirilla?, spirochaetes. 



Hydrodictyon. 



Gomphonema. 



2 Bacilli, bacteria. 



4 Closterium. 



6 Nostoc. 



8 Merista. 



10 Volvox. 



H 



