Mr. G. H. K. Thwaites on the Gonidia of Lichens. 219 
Sargassum Wightii. . 
Fig. 1. Portion of a branch. 
— 2,2. Leaves and vesicles from a young specimen. 
— 3. Raceme of fructification as sometimes seen terminating the 
branches. 
— 4. Portion of a raceme in its more compact form, 
— 5. Portion of do. as seen in fig. 3. 
— 6. Vesicle. 4 & 5 magnified. 
Sargassum cervicorne. 
Fig. 1. One of the fertile ramuli, and leaf given off at the base of a branch. 
_ — 2. Leat from a young plant with.vesicles. 
— 8. Do. from towards the upper part of same plant. 
-— 4. Vesicles. 
— 5. Receptacles as they are developed on one specimen. 
— 6. Do. The last magnified. 
XXV.— On the Gonidia of Lichens. By G. H. K. Tuwairss, 
_ Lecturer on Botany and Vegetable Physiology at the Bristol 
Medical School. 
{ With a Plate. ] 
THERE appears to have been much uncertainty felt by those who 
have devoted their attention to the study of the Lichens, as to 
the real character of those spherical or subspherical green bodies 
which are characteristic of true Lichens, and to which the name 
of gonidia has been given, from the circumstance of their capa- 
bility of becoming developed inte new plants when separated 
from the parent structure. Every one who has examined care- 
fully the thallus of a Lichen under a tolerably high power of the 
microscope, must have been struck by the peculiar appearance of 
the gonidia, as compared with ordinary cellular structure :—the 
frequent irregularity in their form—their want of correspondence 
in size—their slight attachment to each other, or to the filamen- 
tous tissue surrounding them, and their aggregation im certain 
parts of the structure—must have taken the attention of any 
observer who has been much accustomed to the examination of 
vegetable structures. These peculiarities indeed gave rise to a 
strong desire on my part to ascertain the real character of gonidia, 
and after examining a great number of species, both of true 
Lichens and of the genus Collema, and plants allied to it, 1 am 
able with confidence to state what is the true character of gonidia. 
It is pretty generally known that the thallus of Collema consists 
of a number of moniliform filaments, and also of delicate anasto- 
mosing cylindrical filaments immersed in a more or less firm ge- 
latine. When examined more carefully the structure is found 
to consist of numerous Nostoc-like vesicles closely cohering, and 
among which ramify the anastomosing filaments. The cellular 
