AND LIFE-HISTORY OF A TROPICAL EPIPHYLLOUS LICHEN. 95 
when it comes to rest (fig. 47) *. I could not detect a distinct blue coloration with 
iodine, though in some cases they appear to be tinged witha faint rosy violet or mauve hue. 
On several occasions, after lying for from three to twenty hours in water, most of the 
zoospores appeared to have burst; in other cases they lost colour and shrivelled up. 
No attempts to cultivate them have succeeded; and I have never observed them con- 
jugate with one another or with any other body. Whether they are of the nature of 
antherozoids or asexual reproductive zoospores must be considered undetermined. That 
they are zoospores developed by a fertilized oosphere, the ovoid sac being a female repro- 
ductive organ, seems to me in the highest degree improbable, since I cannot think the 
fertilization-process of so relatively large a body can have escaped observation f. 
If we now give attention to the. “ fertile hairs,” the second of the two kinds of sub- 
aerial trichomes shortly referred to above (p. 91), the following facts have been ascer- 
tained concerning their structure and functions. 
I have already stated that these hairs arise from single cells of the thallus. Each com- 
mences as a simple papillar bulging of the upper wall, which grows forth perpendicular 
to the plane of the thallus and leaf, extending apparently by apical growth. Careful 
examination shows that each cell producing one of these structures is definitely situated 
with regard to other cell-series, similarly to those which become metamorphosed into the 
zoospore-producing sacs just described. Each “ fertile hair” springs, in fact, as before, 
from the end cell of a series (cf. Pl. XIX. fig. 15), and therefore concludes the further 
development of that series as a constituent part of the thallus-plate. 
When completely formed, the typical “fertile hair" (fig. 21) consists of a swollen 
thick-walled basal portion, arising from the end cell of a series, as said; and from this 
proceeds a stiff stalk composed of four or five long cylindrical cells, standing freely into 
the air. The uppermost of these supports a swollen subglobular cell (figs. 24 &c.), from 
the sides of which are protruded about ten short curved pedicels, each of which supports 
an ovoid smooth sporangium-like body, filled with dense finely пе protoplasm, 
which later becomes broken up into zoospores. 
All these parts, the basal cell, the several cells comprising the stalk or “ hair," the 
upper swollen subglobular cell, and the pedicels, are firmly and distinctly separated by 
transverse septa one from the other. All contain protoplasm mixed with granules, 
orange-red oily globules, and abundance of starchy matter, such as were met with in the 
thallus-cells. The peculiar thickening of the walls of the basal cell (fig. 25) may 
perhaps be correlated with the necessity for firmness to support the relatively heavy and 
bulky parts above. The thick cell-wall is partially cuticularized, and evidently stratified 
or divided into “ shells." In some cases, at least, the outermost of these “ she 
becomes more or less separated as a sort of sheath, reminding one to a certain extent of 
what occurs in the trichomes of Coleochete 1. The walls of the succeeding cells of the 
hair offer no special peculiarities, excepting that they often possess small irregularities on 
* І have observed a similar phenomenon with the colourless zoospores of Pythiwm gracile as they come to rest 
before germination. 
+ Reference is made below to some statements bearing on this subject. 
i V. Sachs, Text-book, p. 283, 3rd ed.; and Luerssen, Med. Pharm. Botanik, i. р. 110. Pringsheim, Jahrb. f. - 
wiss. Bot. vol. ii. 
SECOND SERIES.—BOTANY, VOL. II. R 
