CHAPTER XIV. 



THE STAMEN AND POLLEN-SAC. 



All the facts brought forward in the preceding chapter may be 

 observed under a hand lens, or under low powers of the microscope. 

 But observation under higher powers is necessary for obtaining an 

 intelligible grasp of the details of propagation in Seed-Plants. The 

 minute structure of the outer envelopes can be dismissed briefly. 

 The sepals, which are usually green and relatively firm in texture, 

 repeat in their structure, though on a reduced scale, the features of 

 foliage leaves. Their epidermis bears stomata, and the mesophyll 

 below, though small in quantity, contains chlorophyll, and is traversed 



Fig. 190. 



Single coll of a petal of Senecio, showing numerous chromoplasts of semi-crystalline 



form. (800.) (After Schimper.) 



by vascular strands after the manner of other leaves. The petals also, 

 though wider in expanse and more delicate in structure, are constructed 

 on a similar plan. But the green of chlorophyll is replaced in them 

 by other colours. The blues and pinks are chiefly due to colouring 

 matters dissolved in the watery cell-sap of the cells. But the red and 

 yellow colours are given by bodies called Chromoplasts. These are 

 often of irregular crystalline form. They are derived from the 

 plastids of the young cell, and multiply like them by fission (Fig. 190). 

 Sometimes both sources of colour may be present in the same petal, 

 and even in the same cell. The streaky colouring of Parrot Tulips 

 arises from the irregular distribution of the chromoplasts in addition 

 to the soluble colouring. The outer floral envelopes take no direct 

 part in propagation. Indirectly they serve that purpose : the sepals 



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