CHAPTER XV. 



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 



fe^sv 



C 



Fig. 200. 



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



form. ( x 800.) (After Schimper.) 



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

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

 though wider in expanse and more delicate in structure, are con- 

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

 them by other colours. The blues, reds and intermediate shades 

 of flowers are due to pigments (Anthocyanins) dissolved in the 



1-sap. Yellow colours are given by pigments confined to bodies 

 called Chromoplasts, which are frequently of irregular crystalline 

 form (Fig. 200). Usually these yellow pigments are the same as 



cur in the leaf, namely Carotin and Xanthophyll (see p. 117). 

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

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

 i from the irregular distribution of the chromoplasts in addition 

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

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



280 



