406 HOFMEISTEB, ON 



into only two unequal cells ; it is probable that the larger 

 of the two is the terminal cell — expanded so as entirely to 

 fill the pollen-cell — of the short row produced by the 

 multiplication of the smaller portion of the pollen-grain.* 



The cell-multiplication in the interior of the pollen-grain 

 of the Coniferse takes place very rapidly ; in the space of a 

 few T days ; I observed it, for instance, in Pinus Larix, 

 in the year 1855, to last from the 27th of March to the 

 10th of April. 



The pollen of the Coniferse passes through the wide 

 micropyle directly on to the nucleus. Each pollen-grain 

 sends out into the tissue of the latter — at first only for a 

 short distance — a tube formed by the prolongation of the 

 terminal cell of the short row of cells attached to its inner 

 wall. In Taxus and Juniperus this tube is emitted shortly 

 after the shedding of the pollen, in the Abietineae not until 

 after remaining dormant for many weeks. The formation 

 of pollen-tubes takes place in Pinus sylvestris, Muglms, and 

 austriaca at the beginning of June, in P. Strobus somewhat 

 later. In a few days they penetrate at the utmost not 

 farther than near to the place where the integument sepa- 

 rates itself from the nucleus (PI. LIX, fig. 14); then, and 

 not unfrequently even sooner, their longitudinal growth 

 ends for the first time (PI. LIX, fig. 17). Up to this point 

 the embryo sac remains a simple cell, whose large nucleus 

 is gradually dissolved (PI. LIX, fig. 14). Some days later 

 however numerous free nuclei appear in its interior 

 (PI. LIX, fig. 15), and immediately thereupon it appears 

 filled by a large number of radially-elongated cells arranged 

 in a concentrical layer (PL LIX, figs. 16, 16*), which mul- 

 tiply actively in all three directions until the commence- 

 ment of the winter rest. The primary wall of the embryo- 

 sac has in the mean time become so thin and delicate that 

 it almost disappears from observation. At the same time 

 a considerable multiplication of all the cells of the nucleus 



* The pollen of Ephedra behaves exactly like that of Larix (see Schacht, 

 c das Mikroskop/ 2nd ed., 1855, p. 148); the pollen of the Cycadeaj on the 

 other hand appears unicellular when ripe. Possibly stages of development 

 similar to those of the Coniferse are gone through in these plants, but are 

 entirely obliterated at an early period. 



