ON PLANT TISSUES. 159 



some future time, making them on the same plants during varying 

 conditions of growth and season, so that, perhaps, some of the 

 plants I have recorded as unaffected may react when experimented 

 on at an earher or later stage of their growth. For instance, 

 some months ago I demonstrated the formation of acicular crys- 

 tals in the leaf of the Brotera mellifera, after heating with water. 

 The field becoming absolutely full of these crystals resembling the 

 pappus heads of a Composite flower ; but now at this season, when 

 the young leaves are making their appearance, I can get no such 

 result. 



There has not been sufficient time to extend observations on 

 the petals of various plants, but I believe a difference will be 

 found in many ; as, for instance, these organs reacting under che- 

 micals, but the hairs of the same plant remaining nearly, if not 

 quite unaffected by the reagent. 



The examination of seeds will prove most interesting, as well 

 as profitable, and experiments in this direction should be duly 

 recorded in some publication devoted to natural history. 



So also this mode of chemical treatment may be extended to 

 the ovules of plants, and perhaps be available in demonstrating 

 the action of pollen tubes. From some slight observations, I 

 think this kind of reaction should be extended to the Fungi — I 

 mean to epiphytal and entophytal forms — so as to endeavour to 

 trace their mycelia in the living tissues, inasmuch as they appear to 

 draw their nutrition from them, and their myceHa^ may yield some 

 colouration, and so lead to their more ready detection. I have 

 not been able to experiment on the Lichens, nor the Algae. Five 

 kinds of Ferns have been tried with differing results. 



It might be supposed that the Ammonia in the reagent pro- 

 duces the changes in the cells ; but I have found Potassium 

 Molybdate and Sodium Molybdate quite as effective. 



Molybdic Acid alone acts feebly in some cases, but by the 

 further addition of Soda or Potassa a rapid and decided reaction 

 has followed. 



I consider we have fair evidence of the colouration being due 

 to the Molybdium. The general mode of treatment is so easy 

 and the results are so remarkable, I feel satisfied this mode of 

 investigation will give work to a class of observers, who, not being 



