141 
on the walls of the old fortifications in San Juan, which to an 
important part consists of c alcareous rocks and offers similar 
conditions for vegetative life 
In the limestone mountains mentioned above, were found 
larger and smaller caves, where according to the depth reigned 
to) 
plete darkness eft genera of algae grew in the places 
the intensity t was most suitable. In somewh 
moderate daylight the r f the caves showed themselves 
oofs 0: 
covered with a layer several millimeters thick of an olive-colore 
mass of slime which belonged to a species of Gloeocapsa; at the 
margins this shaded off into a strongly bluish-green covering, 
which consisted of a species of Chroococcus. Just the same algae 
were found later under the same conditions in a half-dark walled 
genera in the several families: of Chroococcaceae, Chroococcus, 
Sunita, Gloeothece, Aphanothece, and Microcystis; of Lyng- 
bya , Phormidium, Microcoleus, and Schizothrix; of Nosto- 
caceae, i of Rivulariaceae, Calothrix; of Scytonemataceae, 
Scytonema; and of Stigonemataceae, Stigonema. Besides I found 
Chroothece, which belongs to Glaucophyceae, very common. 
It was, however, more common on old walls than on earl 
c 
Unfortunately, I have not had chance to he npr eee the lime- 
stone mountains so thoroughly as they probably deser The 
cause was an illness which hindered me from doing any wee 
for several days during my stay at Arecibo. 
the journey to Utuado on the fourth of March, I collected 
algae practically as limestone lasted. There were 
m. ifferent localities to investigate higher up in the dis- 
trict of eruptive rocks und it more advantageous to 
make a return here from Utuado in order to make a more 
thorough investigation. 
