FERTILIZATION. 313 



SECT. IX. FERTILIZATION. 



571. Many important points respecting the fertilization of the 

 ovule are still unsettled. Our restricted limits forbid an account 

 of the various more or less conflicting views which prevail, or 

 have recently prevailed. The principal disputed questions, how- 

 ever, now relate to the first step in the formation of the embryo. 

 The action of the pollen, through which it is placed in connection 

 with the nucleus of the ovule, is now satisfactorily known. 



57*2. The arrangement and adjustment of parts, mechanical and 

 otherwise, which secure the application of the pollen to the stig- 

 ma, are so extremely diversified in different plants, that we can- 

 not undertake to give even a general account of them here. The 

 adaptation is sometimes in the relative length of the floral organs in 

 connection with the position of the flower, whether erect, inclined, 

 or nodding ; sometimes juxtaposition is effected through transient, 

 and often sudden movements, whether mechanical (by elasticity) 

 or spontaneous, which will be mentioned in another place. Fre- 

 quently the anthers open and the pollen is applied to the stigma 

 while the parts are still approximated in the bud. In monoecious 

 plants the staminate blossoms are commonly situated adjacent to 

 the pistillate, or else raised above them, as in Indian Corn. In dioe- 

 cious plants, as indeed in a vast number of others, much is left to 

 the action of the winds, or of insects, which convey the pollen from 1 

 one blossom to another ; and the immense abundance of pollen, 

 especially in monoecious and dioecious plants, greatly diminishes the 

 chance of failure. The loose papillae, or short projecting hairs of 

 the stigma, and especially the viscous fluid which at this time al- 

 ways moistens its surface, serve to retain the grains of pollen on 

 the stigma when they have once reached it. The following brief 

 statement comprises the essential substance of what is known re- 

 specting the immediate 



573. Action Of the Pollen, The grain of pollen becomes turgid 

 as it absorbs by endosmosis (37) the viscous moisture of the stig- 

 ma : its inner membrane consequently extends, breaks through the 

 scarcely extensible outer coat at some one point (or occasionally 

 at two or three points, Fig. 419), and lengthens into a delicate 

 tube, filled with the liquid and molecular matter (fovillse, 535) that 

 the grain contains. This tube (Fig. 416-419), remaining closed 

 at the extremity, penetrates the loose tissue of the stigma, and is 

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