Page:The Journal of Indian Botany.djvu/127



Portulaca quadrifida, L.—(Cont.). The pith is composed of thin-walled cells filled with starch granules.

The two features, viz : the peripheral position of the aqueous tissue and the central position of the assimilatory tissue near the vascular bundles are quite significant. The acqueous tissue from its peripheral position is able to absorb moisture easily and carry on its function without being disturbed by any other tissue situated outside. It further protects the assimilatory tissue from the injurious effects of intense light and heat.

Were the assimilatory tissue peripheral, the products of assimilation would have to travel a long distance before they could reach the vascular bundles; thus the distribution of the products of assimilation would be greatly retarded. Therefore either the assimilatory tissue should be centrally placed near the vascular tissue or the aqueous tissue should be reduced, so that the distribution of the assimilatory products may go on rapidly.

It is possible that the assimilatory tissue enclosed by an extensive aqueous tissue may not get enough light, but this cannot be helped. As the development of an aqueous tissue is necessary for succulent plants, the central position for the assimilatory tissue is the only position, so that both the tissues can carry on their work without being interfered with by the other.