108 RECORD OF CURRENT RESEARCHES RELATING TO 



nuclear tissue. This violent process necessarily more or less com- 

 pletely disarranges tlie relative position of the contents, and leads to 

 false results, if these are not at the same time checked by other modes 

 of preparation. The greater part of M. Tulasne's errors are due to 

 this defective mode of observation. Hofmeister, Schacht, and others 

 have preferred to make longitudinal sections of the ovule, which they 

 then observed in water or some other liquid. Observations made in 

 this way are sufficiently exact ; but the phenomena of osmose intrude, 

 and cause displacement and destruction of the germinal vesicles and 

 of the other minute structures contained in the sac. The process 

 answers for young states of the ovule, especially if to the water is 

 added about 5 per cent, of sugar. 



Strasburger recommends osmic acid of 1 per cent., which has the 

 property of making the nuclei very visible. The use of this reagent 

 is very advantageous in certain cases ; but, unfortunately, it often 

 produces, with the organic matters contained in the cells that surround 

 the embryo-sac, a black precipitate of such density as to prevent its use. 



Another process, also recommended by Strasburger, is to fix the 

 protoplasm by absolute alcohol. All the organs are by this means 

 reduced to perfect immobility, and the preparation can be preserved 

 for an indefinite time. The tissues become opaque, and must be 

 rendered transparent, for observation, by glycerine or potash. Glyce- 

 rine often makes them too transparent, so as to render the cell-walls 

 invisible. Fixation by alcohol is necessary when the embryo-sac is 

 studied in the nearly adult state ; but it is not advisable in the young 

 state. 



M. Yesque has himself often adopted the plan of covering the 

 blade of the razor with a layer of absolute alcohol, which, instead of 

 destroying its cutting qualities, renders it possible to make much 

 finer sections than with the dry razor. The tissues, which are instan- 

 taneously hardened, offer a better resistance to the knife, and the 

 albuminoid substances do not adhere to the blade. The section 

 should then be placed in a drop of alcohol, to wliich is added, some 

 moments afterwards, glycerine or potash. 



Different reagents are required for each species before com- 

 mencing a serious study. It does not answer to adhere either to a 

 single method of preparation, or to a single reagent. 



Large ovules are easily cut by holding them between the thumb 

 and index-finger of the left hand. All those preparations should be 

 rejected in which the embryo-sac is touched ; for it is possible in that 

 case that some of the nuclei may have escaped. It is, however, some- 

 times useful to examine sections of this kind, as, for example, when 

 studying the nature of the wall of the embryo-sac. 



In the case of very small ovules it is, however, seldom that they 

 can be examined in sections through the integuments. Very fine 

 sections are then made through the ovary, with the chance of raising 

 the integuments and exposing the nucleus or embryo-sac. It is 

 obvious that the position of the ovules must first be observed before 

 determining whether to make transverse or longitudinal sections of 

 the ovary. 



