Volume 18, Issue 1
July 1943, pages 1-19
pp 1-13 July 1943
The development ofCirrhina mrigala illustrates the helpless nature of eggs and fry and stresses the need to devise means to protect them from many dangers to which they are exposed. The eggs are laid during floods which may carry them to places where their fate becomes uncertain. The male sheds its milt in water and there are very great chances of some eggs being left unfertilized. The eggs lie submerged on the grass or sink to the bottom and there is every likelihood of the spawning fields drying up before they are hatched. If, however, the eggs escape all these misfortunes and hatch out in time and run into a pond or stream, there they are likely to fall an easy victim to their enemies, namely, the predaceous fish, frogs and birds. Establishment of nurseries and hatcheries near the spawning grounds could only ensure the development of eggs and fry and lessen the chances of their loss and destruction.
pp 14-19 July 1943
In Leptadenia spartium and L. reticulata there are three phloem regions: (a) the outer normal phloem, (b) the intraxylary or inner phloem, and (c) the interxylary phloem which forms inclusions in the wood.
The patches of intraxylary phloem arise from the pith cells, but in later stages even the xylem parenchyma cells adjacent to the pith take part in their formation. In old stems a cambium is differentiated on the outer faces of these phloem groups and produces some secondary phloem centripetally.
The interxylary phloem, present in the stem, becomes differentiated from groups of thin-walled cells produced centripetally by the cambium. Later the cambium resumes its normal activity with the result that the phloem groups become embedded in the secondary xylem.
Owing to an enlargement of the cells in the island and the fact that it is surrounded on all sides by the woody cells of the xylem, there is often a compression and crushing of the phloem tissues in its centre.
A weak secondary cambium has occasionally been observed to differentiate on one or more than one side of some of the older phloem islands.
A comparison with Strychnos nux-vomica shows that in the latter the islands are always produced centrifugally from the cambium and later become embedded due to the formation of a complementary cambial segment on the outer side, whereas in Leptadenia it is the same cambium which produces both the secondary xylem as well as the phloem on its inner side.