86 THE AMERICAN MONTHLY ' [May, 



drops of your thinned yeast and put them into a tumbler of rain-water and 

 put a few other drops in a thin sj-rup of sugar and rain-water. Set them 

 aside a couple of days. You will then be able to learn some of the things 

 which yeast can do. The two tumblers can best be kept in a warm place, 

 and if they are examined, even after 24 hours, great changes will be found to 

 have occurred. Those' who w^ish may study these changes in advance of our 

 description of them, which will be given hereafter. 



(To be contintied.) 



The application of the paraffin-imbedding method in botany."* 



By J. W. MOLL, 



UTRECHT, HOLLAND. 



It is my purpose to introduce into botanical science the paraffin-imbedding 

 method which zoologists generally have employed for several years with great 

 success. The advantages of this treatment appear w^hen combined with 

 the methods of preservation in arresting protoplasm in its living form, in 

 section cutting, and serial mounting. It not only enables the observer to 

 make sections of very minute and tender objects, but to obtain sections through 

 previously determined parts in consecutive order, and to keep in the relative 

 position in mounting parts which are independent of each other in the section. 

 Thus it is possible to make transverse sections of buds in which the position 

 of the leaves remains unaltered and may be studied with ease. 



This method has not come into use because it has not been properlv com- 

 bined with preservative methods for the especial requirements of vegetable 

 histology. Vegetable parts preserved in alcohol are only w'ith great difficulty 

 permeated with paraffin. On the contrary, those which have been preserved 

 in picric or chromic acid, or their mixture, are readily imbedded. This seems 

 to be connected with the presence of cellulose in the vegetable tissue, which 

 cellulose is somewhat macerated bv the acids. The imbedding method has 

 been tried most commonlv for full-grown tissues, hence its failure ; it is best 

 suited for developing tissues — those containing but little cell-sajD, a thin cell- 

 wall, and much protoplasm, and these are the parts where its help is most 

 needed ; thus in longitudinal sections through the median line of growing 

 points, seiual transverse sections of the same object, etc. The imbedding 

 method can very fortunately be combined with the methods of fixing living 

 protoplasm in general use. Thus, in sections of the growing point, the pi'o- 

 cesses of cell-division, with its several karyo kinetic figuies, and in youngest 

 cells vacuoles can be seen. 



The method employed in a single instance may serve as a guide for other 

 workers, to be varied from as occasions seem to suggest. The object studied 

 was the growing points of primary roots of germinating seeds of a Vicia 

 Faba^ or secondary roots of bulb oi Allhini cepa (grown in water). First, 

 tips of the roots are placed in watery solution (i°o) of chromic acid ; osmic 

 acid, 0.02% ; + acetic acid, o.\%\ to remain in the solution 24-48 hours. 

 Then they are washed well in running water ^ or 6 hours. Then they are 

 put through serial alcohols 20%, 40%", 60%, 80%, 95%, and ioo?o. They are 

 then placed in turpentine, thence to mixture of turpentine and paraffin kept 

 at 30-40° C, and finally to pure paraffin at 50° C. After 6 or 8 hours they 

 ai-e imbedded in a block ready for use. After cutting in ribbons the sections 

 were stuck to the slide by the collodion and oil of cloves mixture, and can 

 now be stained or covered with balsam, covered, and examined. 



* Condensed from Botanical Gazette for January, 1888. 



