Fertilization in Cotlema . 
75i 
figure, and this is of a young carpogone which has not yet developed 
a trichogyne. 
The technique necessary for a cytological study of the Lichens has been 
found very difficult by most investigators. Baur found Endocarpon minia- 
tum the only lichen which he could cut in paraffin. For others he found 
it necessary to cut in celloidin after first saturating the block with glycerine. 
In this way he succeeded in getting sections 10 to 25 microns thick. 
For killing and fixing my material I have used Flemming’s medium 
solution of chrom-osmic acetic acids and a 1 per cent, solution of platinic 
chloride with very satisfactory results. After washing in water, the material 
was dehydrated in the different grades of alcohol. Better results in section- 
ing were obtained if the dehydration was somewhat rapid up to 95 
per cent, alcohol. The use of cedar oil makes the material less brittle than 
xylol or chloroform. The difficulties of other students in this respect were 
probably due to failure to dehydrate perfectly and to secure perfect infiltra- 
tion. I have left the material from eight to twelve hours in cedar oil and 
for the same length of time in equal parts cedar oil and 45 0 paraffin. The 
temperature of the paraffin bath should not greatly exceed the melting 
point of the paraffin. Perfect infiltration has been secured in four to five 
days in melted paraffin before embedding. Serial sections 5 to 25 microns 
thick were cut without any difficulty. Some of the slides were stained with 
Heidenhain’s iron-hematoxylin, but the triple stain of Flemming gave the 
most satisfactory results. 
In microscopic section the thallus is seen, as is well figured by Stahl, to 
be composed of a network of anastomosing fungal hyphae embedded in the 
jelly of the algal symbiont, Nostoc. The Nostoc filaments are much more 
abundant near the surface of the thallus, but are also scattered throughout 
its entire thickness (PI. LXIX, Fig. 1). 
Ascogones are formed as soon as growth begins in the spring, and in 
May or June are very abundant in both early and later stages of develop- 
ment. In lobes of small fruiting thalli about half of the sections (25 microns 
thick) show parts of ascogones. In order to facilitate tracing the asco- 
gones and trichogynes I have cut some sections quite thick. With some 
practice in staining, these thick sections stain very well for cytological 
as well as morphological study. The ascogones are found singly or more 
often in groups of three or four and are usually about a fourth of the thickness 
of the thallus below the upper surface. Carpogones have been found in 
groups in a number of Lichens. In Lecanora subpusca , L., Baur (6) and 
Lindau ( 26 ) found the carpogones in groups of five to ten ; in Endocarpon 
miniatum , L., Baur (6) found three to eight. Except in one instance in 
the Collemas , Stahl found that the apothecia arise from a single carpogone, 
and he has figured the carpogones of Collema as isolated. In Physma 
compaction he found several trichogones in a single apothecium. In this 
