146 Review of Letters 



have no reason to believe that in any of these instances the true origin 

 or office of these cords was even suspected. 



"In a short communication addressed to the editor of the LinnfEO, dated 

 Nov. 1827, and published in the fourth volume of that work, Dr. Ehrenberg 

 gives an account of his observations on the structure of the pollen- 

 masses in Asclepiadese; and states that each grain is furnished with a 

 Cauda or cylindrical tube of great length, directed to the point where 

 the membrane of the pollen-mass opens; which appendage he considers 

 as analogous to the hoymi, or pollen-tube of Amici and Brongniart.* 

 He supposes that these processes exist previously to the application of 

 the i)ollen-mass to the stigmatic surface, which is doubtless incorrect; 

 but Dr. Brown has observed in this family the curious fact, that the 

 application of one portion of the pollen-mass to the stigma causes the 

 production of a pollen-tube from every grain of the mass." 



The experiments of Mr. Corda were made with the coni- 

 ferous tribe. 



" The following positions respecting the mode of impregnation in 

 Conifi rae appear to be established by these observations. 



" 1. The pollen-tube penetrates into the micropyle, (exostome,) and 

 in Pinus the pollen-grains fall directly into it; whence the impregnation 

 is immediate. 



" i. The pollen-tube passes through the exostome into the endostome, 

 passes throujjh the cavity of the secundine, and arrives at 



"3. The nucule; extends through the endostome into its cavity; and 



" 4. By the ejection of the fluid contained in the pollen-grains into the 

 bottom of the nucule, gives the first keim (germ) to the formation of 

 the embryo. 



" 5. The formation and developement of the embryo changes the con- 

 tents of the cellular tissue of the nucule, which becomes fluid, and ap- 

 pears to furnish material for the growth of the embryo, 



" 6. The pollen-tubes remain fixed {to the embryo-sac) sometime after 

 impregnation and the commencement of developement of the embryo 

 in the latter." 



Art. II. Letters about the Hudson River and its Vicinity, 

 written in 1835-6. By A Citizen of New York. 1 vol. 

 small 12mo. pp. 209. New York: Freeman Hunt & Co. 

 Boston: Otis, Broaders &, Co. 1836. 



This collection of letters, amounting to seventeen in number, 

 was originally written for the American Traveller, published in 

 Boston, and was not intended for publication in the present form 

 at the time they were commenced; but the author states, in his 

 prefatory remarks, that from the circulation they have had through 



• " Linnxa. IV. p. 95." 



