SECT. II 



PHYSIOLOGY 



249 



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may be cited Agaricus olcarius, found growing at the foot of olive trees in South 

 Europe, Polyporus sulphuretis and other less familiar Agarics {Ag. igneus, nodilucens, 

 Gardiicri, Myccna illuminans, etc.). The pliosphorescenee of decaying wood is also 

 in part, due to the growth of Fungi or Bacteria, but sometimes to an insect 

 {Ncanura) which reacts in this way wlien disturbed. Harmless phosphorescent 

 Bacteria {Microspira 2)hotogena, Psetidomonas lucifera) occur on phosphorescent fish 

 or meat. According to Molisch Bactey'ium iihospthoreiim {Micrococcus phosplwreus) 

 usually occurs on meat which has been moistened with a 3 per cent solution of 

 common salt and kept at a low temperature. The most important plants taking 

 part in the phosphorescence seen in the sea are Pyrocystis noctiluca, belonging 

 to tlie Gymnodiniaceae and 

 certain Peridineae. Their 

 phosphorescence, according 

 to observations on Ceratium 

 trijjos made by Reinke, is 

 brought about by mechani- 

 cal as well as by thermal 

 and chemical stimuli. 



This phosphorescence at 

 once disappears in an atmos- 

 phere devoid of oxygen, 

 only to reappear on the 

 admission of free oxygen. 

 On this account the phos- 

 phorescent Bacteria, accord- 

 ing to Beyerinck, afford a 

 delicate test for the activity 

 of assimilation. All the 

 circumstances which facili- 

 tate 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 

 }ihosphorescence is not directly dependent upon the respiratory processes. 



The so-called phosphorescence of the Moss Schistostega and of the Flagellate 

 Chromophyton Rosanoffii has nothing in common with actual phosphorescence, but 

 is produced solely by the reflection of the daylight from peculiarly formed cells 

 (cf. Figs. 205, 206). The phosphorescence observed in some seaweeds results, on 

 the other hand, from the fluorescence and opalescence of certain of their albuminous 

 substances, or from the iridescence of their cuticular layers. The latter condition 

 is also found in some Selaginellas. 



^'- 



FiG. 206. — Pliospliorfescent cell of the protonema of SchUtostega. 

 S' S', Path of a ray of light, which, alter passing through the 

 chloroplasts, acquires a green tinge and is totally reflected. 

 (Cf. Fig. 205.) 



Sub-Section II 



DEVELOPMENT 



Development accompanied by changes of form due to growth is 

 one of the most general and striking of the vital phenomena of the 

 plant. A mere increase in volume does not necessarily imply growth 

 for no one would say that a dried and shrivelled turnip grows when 

 it swells in water. Only permanent and irreversible increase of size 



