298 The Microscope. 



has a straight embryo, or even a bent one, it is better to deter- 

 mine by dissection just how its parts are arranged with refer- 

 ence to the external parts or form of the seed. Thus the seeds 

 of Heliantlms tuberosus vre flattened and slightly wedge-shaped. 

 The embryo within is straight, and the upper or inner surface of 

 the cotyledons lie in a plane parallel to the place in which the 

 seed is flattened. Moreover, the cotyledons are in the broader, 

 upper end of the seed. Where the seed has no external char- 

 acter, as in Eupaiorium^ by which the position of its internal 

 parts may be located, one has either to take the chances of get- 

 ting the section in the right plane, or open the coats enough to 

 see how the parts are arranged, and then mark the seed in some 

 way. Having selected well-filled seed, I put them in water at 

 the ordinary temperature of the laboratory for thirty-six hours. 

 From the water they are transferred immediately to weak alco- 

 hol (40 per cent.), and graduall}' hardened by transferring to 

 stronger alcohol until they are in 95-per-cent. alcohol. Next, 

 they are transferred to equal parts of alcohol and chloroform for 

 from four to eight hours, the time depending on the size of the 

 seed. Then, in pure chloroform for the same length of time. 

 Then, for twenty-four hours, into chloroform with as much par- 

 aflfln as it will dissolve at the ordinary temperature. Prom this 

 into paraffin softened with chloroform until the melting point is 

 about 95° Fahrenheit. The specimens are kept in this melted 

 paraffin twenty-four hours. I have always been careful not to 

 let the temperature go above 116° Fahrenheit, although I think 

 it probable that a somewhat higher temperature would not hurt 

 the ttssue of the seed. From this they may be embedded in 

 hard paraffin, and will be found thoroughly infiltrated. 



They may be sectioned in the paraffin blocks either freehand 

 or with a microtome. It is highly essential that the sections be 

 kept in series, and that none of them should be missing. The 

 texture of a seed is so fragile, than when cut in thin sections 

 the least carelessness may spoil the result. 



A very eflfectual way to keep sections intact when they are 

 cut in a paraffin block is that proposed by Dr. Mark {American 

 Naturalist^ 1885, page 628). It consists in collodionizing the 

 object as the sections are taken. Yery thin collodion should be 

 used and applied to the cut surface after each section is taken. 

 Lee ( Vade 3Iecum, page 150) recommends that " the collodion 



