NOTICES OF BOOKS AND MEMOIRS. 279 



watch-glass, and attached to the wall of the grain. This wall is, 

 however, not formed of cellulose, and it soon disa^Dpears, the two 

 nuclei being then found free in the fo villa. After a time each 

 nucleus loses its nucleolus. In Orchids division takes j)lace in 

 flowers at the to^D of a spike wdiile those below are in bloom. 



It is usually difficult to see the nuclei in unprepared grains of 

 Dicotyledons, but they may always be seen in the crushed fovilla ; 

 sometimes, indeed, as in 2lonotropa and liheiun, they may be found 

 without the use of reagents. In this last genus {li. hyhridiun), 

 owing to the absence of starch, the process of division can be 

 followed in a most satisfactory way. The nucleus lies before 

 division in the plasma lining the wall which a few days before 

 pollination becomes massed round it. In segmentation a cell-plate 

 is laid down in the ordinary w^ay, and thus the small " vegetative " 

 cell is separated from its large sister-cell. The free nucleus now 

 wanders away to the other side of the grain, which becomes filled 

 with starch ; finally the plasmatic wall is absorbed, and the two 

 nuclei float freely in the fovilla. The process is seen less clearly in 

 Gloxinia {O. hybrida) on account of the abundance of starch masking 

 it somewhat ; in this -plunt it occurs in buds 22 mm. long. The 

 author has also studied it in Fi/rola, and not having met with 

 a single case in which division did not hold, he comes to the 

 reasonable conclusion that it is of universal occurrence among 

 Metasperms. 



Fii-ed with the desire to ascertain what becomes of these nuclei, 

 the poUen was cultivated in a droi^ of syrup, of various concentration 

 according to the sx^ecies, suspended over a moist chamber, and put 

 in a dark place, as light retards the germmation of pollen."^ The 

 nuclei were seen to pass into the tube, becoming narrower and 

 longer as they advanced. The hinder one in Orchis disappears after 

 a time, and in AUium they sometimes both remain for a while at 

 the mouth of the cell before j)assing into the tube.f There 

 is no regular order of entrance into the tube, sometimes the 

 nucleus of the pollen-cell being first, sometimes that of the vegeta- 

 tive-cell. 



We will now leave the male element after again calling attention 

 to the similarity of the x^henomena which occurs inside the pollen- 

 cells of Metasperms and those of Conifers and Cycads, as well as 

 the microspores < f some higher Cryptogams, to give an account 

 of Strasburger's discoveries a propos of the embryo-sac of Phanero- 

 gams. As types of Monocotyledons, Orchids wxre made use of, and 

 especially Orchis jmUens. The young ovules were placed in 3 per 

 cent, solution of sugar, and in addition, when division was expected, 

 in a di'op of 1 per cent, osmic acid. The following series of 

 developments was then observed : — The great cell of the central row 

 of the nucleus divides into a lower :]: larger and an upper small cell, 



* This fact probably accounts for styles beiug so often more or less terete 

 and not flat, as the tubes growing down a Hat style would be more exposed 

 to liglit. 



+ lu a species of Mimulus we have seen one nucleus at tlie mouth and one 

 a long way in the tube. 



+ That end of the sac nearest the micropyle Ave refer to as the upper. 



