258 METHODS IN PLANT HISTOLOGY 



The white bhsters cause Uttle distortion, but are easily recognized 

 by their color; the oogonia do not cause any change in color, but they 

 cause great distortion in the pods or stems, so that these organs may 

 reach several times their normal size. Parts only slightly distorted 

 should be selected, as well as the extreme cases; otherwise, you will 

 secure only old fertilized eggs, with very few of the younger stages. 

 The stages between B and C of Figure 62 often have numerous mitotic 

 figures, and the divisions are simultaneous. Sections at 3 fx, or less, 

 are better for these figures. The oosporic phase of Albugo hliti is eas- 

 ily recognized on Amaranthus, especially on A. retroflexus, where the 

 oospores may be seen with the naked eye by holding the leaf up to the 

 light. The oospores usually occur in more or less circular patches upon 

 the leaf. When they occur among the floral structures, there is often 

 a slight reddish coloration. Unfortunately for the collector, it is very 

 seldom that any red coloration in Amaranthus is due to the desired 

 material. 



The oosporic stage of Albugo iponieae, on the morning-glory, causes 

 extreziie distortion of the stem. For sections, it is well to cut out small 

 pieces of the cortex, rather than to fix larger pieces of the stem. 



HEMIASCOMYCETES 



Saccharomyces. — Formerly it was considered rather difficult to 

 demonstrate the nucleus of the yeast cell. With fresh-growing yeast 

 the following method by Wager made the classical demonstration. Fix 

 in a saturated aqueous solution of corrosive sublimate for at least 12 

 hours. Wash successively in water, 30 per cent alcohol, 70 per cent 

 alcohol, and methyl alcohol. Place a few drops of alcohol containing 

 the cells on a cover, and when nearly dry add a drop of water. After 

 the yeast cells settle, drain off the water and allow the cells to dry up 

 completely. Place the cover, or slide, with its layer of cells in water 

 for a few seconds, and then stain with a mixture of fuchsin and methyl 

 green, or fuchsin and methyline blue. Mount in glycerin or in balsam. 



With modern methods, there should be no more difficulty than in 

 demonstrating the nucleus in the Cyanophyceae or in the mycelium of 

 the Phycomycetes. Use an abundance of vigorously budding material, 

 so that you can afford to lose most of it and still have a plenty left: 

 fix in the Chicago chromo-acetic-osmic acid solution and stain in iron- 

 alum haematoxylin. Use the Venetian turpentine method, or imbed in 

 paraffin and cut sections at 2 or 3 n. 



