316 Scientific Proceedings, Royal Dublin Society. 



at the latest by March 20th. This early activity is in marked contrast in the 

 Botanic Gardens to the other sluggish pines. 



The tetrad formation in Larix kptohpis presents nothing new. The 

 omission of the second division, as described by Coker, can be confirmed, 

 but prolonged search failed to reveal the permanent adhesion of any such 

 pair of grains. That Coker's interpretation of the origin of the double 

 grains of Larix is, then, erroneous is verified by the appearance found in a 

 later sac, and shown in PL XVII, fig. 14. One grain has divided most 

 irregularly, almost as if it were a complete tetrad which has not separated ; 

 but its position and its shape relative to its fellows show that they are really 

 three from a tetrad, one of which has prematurely divided. 



The exact parallel with Picen, however, is quite clear. Bounding off 

 rapidly, the large nucleus, PI. XVII, fig. 15, remains for a little while in the 

 resting condition. Nucleoli are very distinct and large, and may be in number 

 up to three. Their function is, as usual, in doubt, because when the nucleus 

 is preparing for division the spireme stage may be far advanced and the 

 nucleoli unchanged, PL XVII, fig. 16. By the time the spireme becomes 

 segmented into chromosomes they have disappeared. Evidence as to their 

 extrusion into the cytoplasm was present, but the cytology was not followed. 

 In the majority of grains the first division in the young grain was normal 

 (PL XVII, fig. 17), cutting off a small prothallial cell in which the nucleus 

 and cytoplasm rapidly degenerated in the typical way. The wall was 

 distinctly connected to the intine (PL XVII, fig. 18). If, however, a little 

 more cytoplasm than is usual is cut off, the prothallial nucleus may go to a 

 large resting-stage before slowly degenerating. Such an occurrence is very 

 common, and accounts for the markedly large prothallial cells with definite 

 walls in so many mature grains (PL XVII, fig. 19). 



Sometimes the division and the spindle were oblique (PL XVII, fig. 20), 

 and the result was the cutting off of a cell about one-third of the whole grain 

 (PL XVII, fig. 21). The spindle may be at right angles to its normal 

 position (PL XVII, fig. 22), and the result is the division of the cell into equal 

 or sub-equal cells (PL XVII, fig. 23, and compare figs. 9, 10, 12, 13, PL XVII). 

 Finally, no wall at all may be formed, leaving two nuclei free in the 

 cytoplasm (PL XVII, fig. 24). This is exactly the course of things in Picea 

 caimdensis (7). We may presume a similar course in Abies (8). 



After division, the primary nucleus returns to the resting condition 

 (PL XVII, fig. 18), and then resuming, almost invariably cuts off a cell which 

 rapidly passes into a typical degenerated prothallial cell. PL XVIII, fig. 1, 

 shows the normal condition. The second prothallial wall is always an out- 

 growth, as it were, from the first and is equally distinct. If the first division 



