74 



THE AMERICAN MONTHLY 



[Apra, 



colorless vacuole, Thallus crusta- 

 ceous, hard, verrucose, pale green, 

 radiately striate within. Cells borne 

 singly or in pairs on gelatinous 

 stems, tubular, di- or tri-chotomously 

 branched, fastigiate, densely com- 

 pacted, calcareous. Division alter- 

 nately in two directions. 



[ To be continued^ 

 O 



Pollen-tubes. 



The number of the yb^rwa/ of the 

 New-York Microscopical Society of 

 January, 1885, contains an account 

 of the proceedings at their meeting 

 of November 21st, and also a paper 

 read by Mr. N. L. Britton, to which 

 he gives the title, ' Criticism on Mr. 

 J. Kruttschnitt's Papei's and Prepara- 

 tions relating to Pollen-tubes.' 



Mr. Britton's remarks can scarcely 

 be taken as a criticism ; they seem to be 

 rather intended as a hint that an ama- 

 teur worker in a science should not 

 annoy the professors thereof by per- 

 sistently calling into question the in- 

 fallibility of their dogmas and their 

 teachings. 



I am not inclined to take the hint, 

 notwithstanding the formidable array 

 of heavy artillery brought to bear 

 against me. I will not haul down my 

 colors ; I will only do so on condition 

 that Mr. Britton, or any one else, pro- 

 duce a preparation in which the pol- 

 len-tubes as they are emitted on the 

 stigma of any angiospermous plant 

 may be traced down the style to the 

 ovarian cavity and to the micropyle 

 of the ovules. This should not be a 

 difficult task, considering what Mr. 

 C. R. Barnes, professor of natural 

 history at Purdue University, La 

 Fayette, Ind. , says on this subject. In 

 a letter received from him on the 22d 

 of May last occurs the following : 

 ' There is a plant in which you can 

 easily see the entrance of the pollen- 

 tubes into the micropyle, that is, if 

 you are as successful as my students 

 usually are. That plant is Caf sella 

 Bursa-pastoris.^ I sent him some of 

 my preparations, requesting him to 

 send me some of his ; in answer he 



writes under date of June 4th : ' I 

 am just now in the very busy time of 

 commencement, but as soon as that 

 is over I shall send you a slide show- 

 ing the entrance of the pollen-tube 

 into the micropyle of an ovule of 

 Capsella. They are so easily gotten 

 when wanted that I have never 

 thought worth while to make a per- 

 manent preparation.' So far Prof. 

 Barnes has not redeemed his promise ; 

 I, however, in the interval, have 

 made a number of preparations, in 

 fact, I have subjected Capsella to a 

 most thorough examination in the 

 various phases of development of its 

 ovaries, but have failed to discover 

 anything having the appearance of a 

 pollen-tube, such as the pollen-grains 

 of certain plants emit on the stigmas. 

 I am therefore at a loss to imagine to 

 what structure Prof. Barnes attaches 

 the significance of a pollen-tube, un- 

 less he take as such the vascular fibre 

 in the funiculus. 



The difference of opinion concern- 

 ing the fecundation of the ovules refers 

 appai'ently to the functions which are 

 attributed to the conducting tissue. 

 All admit that the conducting tissue 

 performs a part herein ; some assign 

 it only a subordinate one, making it 

 the carrier of the pollen-tubes towards 

 the micropyle, whilst I consider it 

 the principal factor, in as much as it 

 diffuses the fertilizing element of the 

 pollen all over the whole ovary in its 

 entirety to the extent of its ramifica- 

 tions. Mr. Britton, on the authority 

 of Mr. Sachs, says : ' The pollen- 

 grains which germinate on the stigma 

 send out their tubes through the chan- 

 nel of the style, where there is one, 

 or more frequently through the loose 

 conducting tissue in its interior down 

 to the cavity of the ovary.' 



The examination of the style and 

 of the ovary of Cereus grandijlora 

 shows unmistakably the functions as- 

 signed in this plant to the conducting 

 tissue. The pollen-tubes, after their 

 emission on the stigma, insinuate 

 themselves amongst the papillae of 

 the stigma where their contents, the 



