1882.] the Pollinium in Asclepias. 295 



some of the aniline colours, viz. Gentian-violet, Saffranin and 

 Methyl-green (to the latter of which a few drops of solution of 

 Acetic Acid, one per cent, strength, had been previously added), 

 to detect not a single nucleus only, but two nuclei one of which 

 was invariably larger than the other. 



The smaller nucleus was often found lying close to the cell- 

 wall, and in these cases I believe that, surrounded by a small 

 quantity of protoplasm, it is cut off from the rest of the grain by 

 a cellulose-wall although I was not always able to shew this 

 satisfactorily. This discovery is especially of interest in con- 

 nection with the recent researches of Strasburger 1 and Elfving 2 

 since further confirmation of their observations has thereby been 

 obtained in the pollen-grains of plants which they did not in- 

 vestigate, and in which the very presence of nuclei of any kind 

 whatever had not been previously detected. I consider the smaller 

 nucleus of the Asclepiad pollen-grain to be the representative 

 of what Elfving terms the " vegetative nucleus " and others have 

 dignified as the "passive nucleus," which nucleus is genetically 

 the last remnant of the male prothallium of a Vascular Cryptogam 

 type such as Equisetum ; while the larger nucleus, equivalent to 

 the " active nucleus ", is genetically the last remnant of the 

 antheridium of such a type. 



In shape the pollen-grains are always nearly spherical, though 

 usually slightly angular, so as to be really irregularly polyhedral ; 

 their membrane, is as previously stated, single, very thin at first, 

 ultimately becoming thicker, smooth hyaline and transparent, and 

 formed of unchanged cellulose 3 . There is at this stage no ap- 

 pearance whatever of the tubes which are afterwards produced. 



Strasburger 4 , in his most recentty published work, mentions 

 the fact that he has observed the presence of only a single coat 

 in the pollen grains of the following plants — Gaura biennis L., 

 Clarkia elegans Dough. Senecio vulgaris L., Cobcea scandens Cav., 

 Allium L. JS'aias major 5 ?, and Orchids, and the same phenomenon 

 was described by Fritzsche 6 , and has long been known to occur in 



1 " Ueber Befruchtimg unci Zelltheilung." Jenaische Zeitschrift fiir Natur- 

 icissenschaft, Bel. xi, Neue Folge, Bd. iv. 1877, Heft iv. page 460. 



2 Jenaische Zeitschrift fur Naturwissenschaft, 1879i part i., and Quarterly 

 Journalof Microscopical Science, N. S. Vol. xx. 1880, pp. 19 to 35. 



3 I have never seen it present the irregular internal thickenings which are 

 frequent in the pollen-grains of some plants, e.g. Cucurbita, and which are there 

 used subsequently in the formation of the pollen-tube. 



4 Ueber den Bau and das Waehsthum der Zellhaute, Jena, 1882. 



6 Ueber den Pollen. — Mcmoire presents a V Academic impcriale des Sciences de 

 St PStersbourg, iii. 1837. 



6 Hofmeister (Neue Beitriirje, 1859, part ii.) describes the existence of " a very 

 thin but distinct extine " in the pollen-grains of this species, but in his figure, 

 pi. i. .fig. 11, he represents this extine as extending with the intine along the course 

 of the pollen-tube produced from the grain ! It is therefore highly probable that 

 Strasburger's observation is more accurate. 



