Pr.UTILlZATlON. 121 



goin^' important changes. The stigtnatic surface assumes 

 an irrcnilar, granular appearance, becouiing more lax in its 

 texture, and secreting a viscid fluid, all of which is accom- 

 plished by the time the pollen is perlected. The pollen ilum 

 falls upon the stigma, is made to cohere by this viscidity, 

 and moistened by the secreted fluid. 



151. Afier the grains of pollen have remained upon tlie moist 

 sti'Muatic surt'ace for several hours, the extine bursts at one or 

 more points, and through the apertures tiie entine is pro- 

 truded containing the contents of the pollen grain. These 

 pollen tubes penetrate the lax tissue of the stigma, and make 

 their wav through the whole length of the style, to the ovule, 

 and reach, and piobiMy in all casesenter, the foramen. The 

 remarkable exhibitions of design for accomplishing this object, 

 are unsurpassed by any phenomena in nature, and the re- 

 searches of Brown, Amici, and Brogniart, have laid open a 

 field wbicii cannot be viewed by a lover of nature, ^^ilh any 

 other feelings, than those of unmingled delight. 



152. Wehavelbund the liibiscusgrandiflora the best example 

 for tracing the pollen tubes of any plant, which we have ex- 

 amined in this respect By examining the |)lant during the 

 dav of the cx[)ansion of the flower, the pollen will be found in 

 abundance on the stigmas, of which there arc five, and 

 tubes will be found to have projected from some of them, per- 

 haps one onlv iVom some grains, and none from others. By 

 the followinj; dav the tubes will have entered the stiirma, and 

 have passed down thcconductingtissueofthestyle, and entered 

 the placenta. The ovule of the Hibiscus is of the campulitro- 

 pour kind, so that the foramen is of course brought round 

 near to the placenta ; and that the pollen tubes may have ac- 

 cess to the foramen, the funiculus is extemled beyond the 

 hilum, so as to pass over the foramen, and thus afford a pas- 

 sage for the pollen tubes into it. Owing to the imperfections 

 of our instrum'^nts during the flowering of the Hibisccs. we 

 could not satisfy ourselves in tracing the tubes farther than to 

 the placenta, though we believe we could discover them at the 

 entrance of the foramen, at a short distance in which they 

 were lost to our observation. "We are obliged on this subject 

 to give the observations of others, not having been able to ver- 

 ify in many points, the facts recorded, from not having in sea- 

 son possessed a microscope of sufficient accuracy and |)0wer, 

 to exhibit the parts with .satisfactory distinctness. Of the pas- 

 sage of the tubes to the placenta, and the molecular constitu- 

 tion of their contents* we can speak with confidence, but as 

 to their course and modifications afterwards, we trust to the 



u 



