4 1 2 MORPHOLOGY. 



Limnantkes I}ouglasii t Linum pallescens, Tropceolum maj us, Cicer arie- 

 tinum, Phaseolus vulgaris, (Enothera viminea, crassipes, rhizocarpa 

 (Plate VI. figs. 7, 8.), Martynia diandra (Plate VI. figs, o, 6.), Salvia 

 bicolor (Plate VI. figs. 3, 4.), Lathrcea Squamaria, Veronica hedercRfolia, 

 serpyUifolia, Pedicularis palustris, Cynanclmm nigrum, Campcmula 

 Medium, Tctragonia expansa, Epilobium hirsutum (Plate V. figs. 7, 8.). 



In many of these plants I have laboured in vain for many years ; in 

 some I have oftener succeeded in observing the whole process without 

 the possibility of deception : I have never yet found any plants in which 

 the observation is so easy, that I could say that I could at any time 

 prepare the necessary dissection with certainty ; I have found it easiest 

 in CEnothera, Veronica, Pedicularis, and the Orc/iidacece. If Santalum 

 album were at our command, we should probably have a plant in which 

 we could at any time demonstrate the process with certainty. Perfect 

 confirmation of the main point, namely, the conversion of the end of the 

 pollen-tube into the embryo through internal processes of vegetation, 

 have been furnished by Wydler* in some species of Scrophularia, by 

 Meyen f in Fritillaria imperialis and Tulipa, and by GelesnofFJ in 

 Amygdalus persica, Iberis amara and umbellata. The observation of 

 Meyen is the better evidence that it came certainly quite unsought for ; 

 since it is alone quite sufficient to refute his very artificial, ancl, I will 

 openly confess, to me thoroughly incomprehensible, explanation of his 

 other less perfect observations. The figures 37 43. Plate XIII., from 

 Alsine media, of Meyen, also agree tolerably perfectly with my observa- 

 tions, only I do not rightly know what to make of figures 38 to 41. I 

 must confess that it has hitherto always appeared to me impossible to 

 prepare it free in so early a condition in Alsine media, and these obser- 

 vations do not at all agree with Meyen's explanation ; moreover, figs. 

 21 23. from Draba verna, fig. 34. from Orchis Morio, fig. 44. from 

 Helianthcmum canariense, fig. 48, 49. from the same plant, only the 

 order is evidently different ; fig. 49 is an earlier condition, fig. 48 the 

 commencement of the constriction of the pollen-tube ; lastly, also, 

 (Polyembryonie, &c., Plate I.), from Viscum album, on which I will 

 merely notice that fig. 8. is evidently later impregnated, and an earlier 

 stage of formation than fig. 7., which follows from the fact that the 

 membrane of the embryo-sac is not yet completely absorbed, and there- 

 fore still surrounds the contained cells with a smooth outline. All the 

 rest of Meyen's figures exhibit only later conditions, after the separation 

 of the pollen-tube outside the embryo-sac, often even after the separation 

 of the germinal vesicle inside it. Lastly, Griffith has instituted researches 

 on this process in Santalum album, and indeed earlier, before my obser- 

 vations were made known ; unfortunately, he evidently had not a good 

 microscope at his command, and he is candid enough not to describe, or 

 draw as definitely seen, anything which remained indistinct to him. 

 Santalum album is* certainly a most advantageous plant for these 

 researches. The allied species of Thesium present great difficulty. 

 On the other hand, Martius||, in the year 1844, published the following 

 passage of a letter from Griffith : " A year ago I sent an extended essay 



* Loc. cit. 



f Physiologic, vol. iii. ; and Uebcr den Befruchtungsact und die Polyembrionie, &c. 

 Berlin, 1840. 



J Botan. Zt'itung, vol. i. p. 841. 



On the Ovulum of Santalum album, Trans. Roy. Soc. vol. xviii. 



|| Munich gel. Anzeig. No. cxliii. p. 107. 



