July, 1899.] 145 



THE IRISH CHARACE^. 



BY PROF. T. JOHNSON, D.SC, F.I<.S. 

 (Read before the Dublin Naturalists' Field Club, November 8th, 1898.) 



The Characeae or Brittle-star plants form a group which 

 has probably had, as regards its systematic position, a more 

 chequered history than any other group. Though now 

 generally regarded as an anomalous group of green algae the 

 Characeae were once by many, and are still by a few, regarded 

 as on a level with the Flowering plants. This view is due to 

 the regularity of arrangement of tbe parts of the plant body, 

 to their high degree of differentiation, and to insufficient 

 knowledge of the exact nature of the reproductive organs. 

 There are many flowering plants with a very poorly developed 

 plant-body, yet by their reproductive organs recognised at 

 once as true flowering plants. 



The sub-kingdom Thallophyta (Algae, Fungi and L,ichens) 

 consists of plants which have, as a rule, no marked division 

 of the plant-body or "thallus" into stem, leaf, and roots. 

 The Characeae stand out from most Thallophyta by the 

 possession of a marked differentiation of the plant-body, which 

 shows a diagrammatic regularity of arrangement into stem, 

 leaf and root. The stem grows by a well-marked apical cell, 

 from which segments are regularly cut off with a definite 

 future history. In the stem one recognises nodes and inter- 

 nodes, stipulate leaves in whorls or circles, and branches, as 

 in an ordinary flowering plant. Though called stem, leaf, 

 etc., the organs have no morphological connection with the 

 stem and leaves of the higher plants. They belong to another 

 generation and cannot be truly compared. The apical bud 

 serves as an excellent object for dissection under the simple 

 microscope ; carefully done, the apical cell and the cells cut off 

 from it can be seen. In the stem of the Characeae there is no 

 suggestion of the veins or conducting strands of the higher 

 plants. The internode consists of one long cell, surrounded 

 in Chara by a many-celled cortex which is often more or less 

 encrusted with chalk or carbonate of lime. In Nitella there 



