224 



THE FLOWER 



must not be confounded with it.) The pollen tube con- 

 tinues to elongate until it passes down through the base of 



the style into the ovary (Fig. 



443, m]. 



326. Course of the Pollen Tube. 

 The time taken for the tube to 

 penetrate to the ovary varies in 

 different flowers 

 according to the 

 distance traversed 

 and the rate of 

 growth. In the 

 crocus it takes 

 from one to three 



443. Diagram of a simple 



flower, showing course of the d m the spot . 



pollen tube: a, transverse J i 



section of an anther before its ted Calla \AfTtM 

 dehiscence; b, an anther de- wiftculcituni} about 

 hiscing longitudinally, with 



pollen; c, filament; d, base of five days, and in 

 floral leaves; e, nectaries; / 

 wall of carpels ; g, style ; h, 

 stigma; i, germinating pollen 

 grains ; m, a pollen tube which 

 has reached and entered the 

 micropyle of the ovule; n, 

 funicle of ovule; a, its base; ^ ^^ ^.^ ^ ^^ ^ ^ 



can not well exceed twenty-four 



orchids, from ten 

 to thirty days. In 

 the hibiscus and 

 many others of 



444. A pollen 

 grain emitting a tube 

 (magnified). 



antipodal cells; v, synergidae; 

 2, oosphere. 



/, outer integument ; q, inner 

 integument; s, nucellus of 

 ovule ; /, cavity of the embryo n r n 



sac; , its basal portion with hours, as the corolla usually falls 

 away on the evening of the day on 

 which it expanded, carrying the 



style and stamens with it, so that if the pollen tube had 

 not reached the ovary by that time it could never 'get 

 there at all. Sometimes the pistil is hollow, affording a 

 free passage to the pollen tube ; in other cases it is solid 

 and the growing tube eats its way down, as it were, feed- 

 ing upon the substance of the pistil as it grows. How is 

 it in the flower you are examining ? In some orchids the 

 pollen tubes can be seen by the unaided eye, massed 

 together within the thickened style, looking like a strand 

 of fine white floss. It takes a grain of pollen to fertilize 



