AMftKft 



J 



300 PHOTOSYNTHETIC SYSTEM 



surface of the plant-body, the presence of a protective epidermal layer 

 being generally unnecessary in the case of submerged plants. The 

 influence of the principle of maximum exposure of surface may account 

 for the fact, that the photosynthetic cells are frequently very small, the 

 total cell-wall-surface available for display of chromatophores being cor- 

 respondingly increased. The principle of expeditious translocation also 

 makes itself felt to a varying extent. Wille 154 indeed has succeeded 

 in finding examples among Algae, not only of all the main systems of 

 construction recognised by the author in the case of the Higher Plants, 

 but also of many of the individual types of arrangement that have been 

 described above. Thus in a number of types {e.g., the Ulva,- Polysiphonia- 



and Lithoderma-types) the 

 photosynthetic and efferent 

 tissues are identical. In 

 another series of genera 

 {Chorda, Chord aria, Dcsma- 

 rcstia, Dictyota, Ahnfeltia, 

 Ccramium, Corallina, Fur- 

 cellaria, Odonthalia, Rhodo- 

 mela) the synthetic products 

 are transferred directly from 

 the photosynthetic elements 



Photosynthetic system of Gelid mm corneum. The photo- . 



synthetic elements (cavities shaded) are arranged in radial to the COnductin a tissue. 

 series converging towards funnel-shaped collecting-cells, 



which in their turn communicate with the conducting Several forms finally (NotJlO- 

 system. ' J v 



gcnia, Bhodophyllis, Crypto- 

 siphonia), conform to the third system, in which distinct intermediary 

 elements are interpolated between the photosynthetic and translocatory 

 tissues. Palisade-tissue appears first in the second of the above- 

 mentioned groups {e.g. in Odonthalia dcntata) ; but the resemblance to 

 the Higher Plants is greatest, where the photosynthetic cells are 

 elongated at right angles to the surface or arranged in anticlinal 

 series and converge towards funnel-shaped collecting cells {Gelidium 

 corneum, Fig. 125), or where the intermediary elements are disposed so 

 as to form curved translocatory paths {Cryptosiphonia Grayana, Ca- 

 losiphonia Finisterrae), just as in the leaves of many Phanerogams. 



VI. ONTOGENY OF THE PHOTOSYNTHETIC SYSTEM. 



In the great majority of cases, the photosynthetic system develops, 

 like other purely parenchymatous systems, from the fundamental 

 meristem. In Cyperus pannonicus, however, the layer of palisade cells 

 that is interpolated between each subepidermal fibrous strand and its 

 associated mestome-bundle arises from procambial elements ; here, 



Fig. 12 



