to the Plant Cell. 
5i7 
For staining the microscopical sections of root tips, the best results were 
obtained from the use of Mann’s Eosin and Toluidin Blue, according to 
a method which I have described elsewhere (Reed, ’04). 
IV. Data obtained from Experimental Work. 
1. Experiments upon the role of potassium. 
The paramount importance of potassium for the production of carbo- 
hydrates in the plant, as well as for the synthesis of proteids, renders its 
study of primary interest. My results agree with those of other investigators 
in showing that potassium is indispensable for the continued growth and 
normal functioning of plants. Even when carbohydrates, like sugar, are 
supplied to most Fungi, they are unable to form proteids in the absence of 
potassium, except in the few instances where rubidium may be substituted 
for it. 
From the standpoint of the experimenter, it is difficult to ascertain 
what will happen when plants are totally deprived of potassium salts. In 
the first place there is always a small amount of potassium in some form 
in the seed or spore from which the plant originates. Knowing, as we do, 
the power of the plant to use repeatedly the same supply of potassium for 
different purposes, one must not disregard the value of a small supply of 
that element. In the section of this paper dealing with methods, it has 
been already indicated that the small amount of potassium in the glass-ware 
which is continuously soluble is capable of partially supplying the needs of 
the plant grown in a culture solution in a glass vessel. 
In a series of cultures of moss protonema where potassium was 
purposely omitted from part of the solutions, I eliminated, so far as 
possible, the amount of potassium originally present. Specimens of a moss 
(Atrichum sp.) bearing mature sporogonia were collected in January. They 
were kept in a dry condition in the laboratory until March 9, when they 
were used in making cultures. By means of sterile pincers and needle, the 
contents of mature capsules were scraped out upon a sterile slide, and at 
once transferred to the culture solutions. The cultures stood before an 
east window in light of moderate intensity, where the temperature ranged 
between 8° and 15° C. 
At the expiration of a month the spores in the control cultures were 
found to have germinated, and to have produced healthy green protonemata 
varying from 2 to 5 millimeters in length. The filaments of the protone- 
borax carmin. (3) It is then stained for two and one-half to three hours in a strong blue-black 
solution of nigrosin in 50 per cent, alcohol which contains acetic acid equivalent to 5 per cent, of 
the entire volume. (4) Decolorization is effected with 70 per cent, alcohol ; (5) then dehydrate 
with absolute alcohol, clear in clove oil and mount in balsam. If the amount of material is small 
the first two processes may be carried through on a slide, but the third is best done in a watch-glass 
or other covered receptacle. 
