sect, ii PHYSIOLOGY 223 



Phosphorescence. — The same conditions which accompany respira- 

 tion also give rise to the production of light or phosphorescence in a 

 limited number of plants, particularly in Fungi and Bacteria. This 

 phosphorescence at once disappears in an atmosphere devoid of oxygen, 

 only to reappear on the admission of free oxygen. All the circum- 

 stances which facilitate respiration intensify phosphorescence ; the 

 converse of this is also true. According to the results of investigations 

 concerning the phosphorescence of animals, from which that of plants 

 does not probably differ in principle, the phosphorescence is not 

 directly dependent upon the respiratory processes, but is due to the 

 production by the protoplasm of a special colloid substance in the 

 form of globules or granules, which give out light when undergoing 

 crystallisation. On free exposure to the atmosphere, and under proper 

 conditions of moisture and temperature, this phosphorescent substance, 

 even after its removal from the living organism, is still capable of 

 giving out light for a long time. 



The best - known phosphorescent plants are certain forms of 

 Bacteria which develop on the surface of fish and meat, and the 

 mycelium, formerly described as " Rhizomorpha," of the fungus Agaricus 

 melleus. As further examples of spontaneously luminous Fungi may be 

 cited Agaricus olearius, found growing at the foot of olive trees in 

 South Europe, and other less familiar Agarics (Ag. igneus, noctilucens, 

 Gardiieri, etc.). The phosphorescence of decaying wood is also, without 

 doubt, due to the growth of Fungi or Bacteria. Of plants taking 

 part in the phosphorescence seen in water, the most important are 

 Pyrocystis noctiluca, an Alga, and the spontaneously luminous Bacteria. 



The so-called phosphorescence of the Moss, Schistostega, and of some Selaginellas 

 and Ferns, has nothing in common with actual phosphorescence, but is produced 

 solely by the reflection of the daylight from peculiarly formed cells (Fig. 325). 

 The phosphorescence observed in some sea-weeds results, on the other hand, from 

 the fluorescence and opalescence of certain of their albuminous substances, or from 

 the iridescence of their cuticular layers. 



IV. Growth 



The size which plants may attain varies enormously. A Mush- 

 room seems immeasurably large in contrast with a Micrococcus, but 

 inexpressibly small if compared with a lofty Californian Sequoia. A 

 Bacillus of the size of a Mushroom, or a Mould-Fungus of the height of 

 a Sequoia, are, with their given organisation, physiologically as incon- 

 ceivable as a Mushroom with the minuteness of a Micrococcus. The 

 size of an organism accordingly is an expression of its distinct individu- 

 ality, and stands in the closest relation to structure and conditions of 

 life, and in each individual varies within certain narrow limits. 



However large a plant may be, and however innumerable the 

 number of its cells, it nevertheless began its existence as a single cell, 



