280 PHOTOSYNTHETIC SYSTEM 



arm-palisade-cell of Anemone sylvestris, and 148 for a four-armed cell 



of Sambucus nigra. The interpolation of complete partitions is of course 



even more effective. 



Quite a unique method of surface-increase is employed in the leaves 



of certain Hymenophyllaceae (Trichomanes aurictdatum, Hymenophyl- 



lum Karstenianum, H. speciosum, H. 

 plumosum, H. Malingii). Mettenius long 

 ago noted that the external walls of 

 the photosynthetic cells which are here 

 superficial project in the form of 

 papillae provided with a dense peri- 

 pheral layer of chloroplasts. In Hy- 

 menophyllum Malingii the papillae are 

 fio. in. two to four times longer than their 



t.s. through a pinna of Hymenophyiium width, and altogether closely resemble 



Malingii. After Giesunhagen. .. . .. / . 



palisade-cells (Fig. 111). It might, in 

 fact, be maintained that the palisade-layer of this plant is composed of 

 trichomes. 



B. THE PRINCIPLE OF EXPEDITIOUS TRANSLOCATION. 



Attention must next be directed to the second principle that 

 governs the construction of the photosynthetic system, namely, the 

 principle of expeditious translocation. It is this principle that deter- 

 mines the orientation of the flanges or partitions which owe their 

 existence to the influence of the first principle, while the great diversity 

 that characterises the detailed structure of the photosynthetic system 

 depends above all upon the fact that this second principle is carried 

 out to a very varying extent in different plants. 



The activity of photosynthetic cells obviously cannot long remain 

 uninterrupted unless the products of synthesis are quickly removed 

 from the place of their formation. Under ideal conditions each 

 individual chlorophyll-corpuscle should be entirely engaged in the 

 formation of starch from the products of its own photosynthetic 

 activity, and should have little or nothing to do with imported 

 carbohydrate material. It is a well-known fact that every chemical 

 reaction proceeds most smoothly and completely, as well as with the 

 greatest velocity, when the products of the reaction are removed as 

 fast as they are formed ; for this reason alone, it is a disadvantage if 

 the products of synthesis are denied immediate egress from the 

 photosynthetic element, while still greater harm results if they are 

 permitted to circulate in the cell, or are actually deposited therein. 

 It is, indeed, a general law of vegetable physiology, that a metabolic 

 process can only be carried on continuously so long as the products are 



