ARRANGEMENT OF STORAGE-CELLS 



423 



elements are isodiametric, and form a dense and irregular mass of 

 cells, the arrangement of which seems to be devoid either of mechanical 

 or of nutritive significance. This type of tissue which may be com- 

 pared to the simplest of the various forms of photosynthetic tissue 

 occurs, for example, in the cotyledon of the Bean, Pea, Oak and 

 Horse-chestnut, and in tuberous storage-organs. Very often, how- 

 ever, the cells of storage-tissues are elongated and arranged in rows, 

 which may be straight or curved, their exact disposition being deter- 

 mined with reference either to the 

 mechanical requirements of the storage- 

 tissue, or to the nutritive arrangements 

 of the embryo [or other developing 

 structure] which is destined to make 

 use of the stored materials. In some 

 cases a single system of curved cell-series 

 serves both to increase the incompressi- 

 bility of the tissue as a whole (mechanical 

 function), and to facilitate the access of 

 food-material to the embryo (nutritive 

 function). In other instances these 

 functions are distributed in accordance 

 with the principle of division of labour 

 between two distinct systems of curved 

 cell-series, which are located in different 

 parts of the storage-organ. A few 

 examples will enable us to apprehend 

 more clearly the precise significance of 

 these statements. 



One of the adjoining figures (Fig. 

 164 c) depicts the greater portion of a 

 transverse section across a mericarp of 

 Anethum Sova. It will be noticed 



that, on the dorsal and ventral sides of the embryo the coty- 

 ledons of which are seen in transverse section at e the endosperm 

 cells form curved series converging towards the centrally situated 

 embryo. The lines of curvature correspond to the planes of compres- 

 sion in two dome-shaped structures placed back to back, an arrange- 

 ment which must considerably increase the incompressibility of the 

 fruit in the antero-posterior plane {i.e. in the direction a-h). As a 

 matter of fact, it is precisely in this plane that the fruit is subjected 

 to the greatest pressure when it swells through absorption of water. 

 If a fairly thick transverse section of a mericarp is caused to swell, the 

 antero-posterior diameter of the endosperm will be found to increase by 



Fig. 104. 



A. Tangential L.S. through a seed of 

 Iris sp. ; e, embryo. x5. B. T.S. through 

 the same seed, taken along the line a-b 

 (in A), x 14 C. T.S. through a meri- 

 carn of Anethum Sova; e, embryo, in 

 all three figures the course of the cell- 

 rows of the endosperm-tissue is indicated 

 by lines. 



