GEM 
Appendix concerning the Use of the Quad- 
rant, Fore-staff, and Nocturnal,” octavo ; 
u Oratio in Laudem Gassendi Astronomi®, 
habita in Aula JEdis Christi, Oxon ,” and 
of several unpublished MSS. on the Doc- 
trine of Eclipses, Lunar Astronomy, Ship 
Building, &c. 
GEMINI, the Twins, in astronomy, one 
of the twelve signs of the zodiac, the thu d 
in order, beginning with aries. See Astro- 
nomy. 
GEMMA (Reinier), a learned Dutch 
physician and mathematician in the six- 
teenth century, was born at Dockunt, in 
Friesland, in the year 1508. He was edu- 
cated to the medical science, of which he 
became a professor in the university of 
Louvain. But Ire was particularly eminent 
for his proficiency in mathematics and 
astronomy, which he taught with distin- 
guished reputation, and the character of 
being one of the best astronomers of his 
time. The fame of his great scientific 
knowledge, and of the v excellent instru- 
ments which he made use of in the illustra- 
tion of it, occasioned his being frequently 
invited to the court of the Emperor Charles 
V. ; but he always modestly declined the 
overtures made to him, preferring the tran- 
quillity. of his literary retreat to the ho- 
nours which he might expect from princely 
favour. He died at Lauvaih, in 1555, when 
only forty-seven years of age. He has 
sometimes had the surname of Friscius 
given him, from the country in which he was 
born. The most celebrated of his works 
were “ Methodus Arithmetic® u De usu 
Annuli Astronomici “ De Locorum des- 
cribendorum Ratione, deque Distantiis 
eorum inveniendis “ Libelius de Prinei- 
piis Astrononiiae et Cosmographia,” &c. 
u Demonstrationes Geometric® de usu 
Radii Astronomici,” &c, ; and “ De Astro- 
labio Catholico Liber.” 
The author had a son, named Cornelius, 
who was born at Louvain, in 1535, and died 
in 1579. He was a poet, philosopher, and 
physician, and taught the mathematical 
sciences at Louvain with considerable re- 
putation. He was the author of “ De Arte 
Cyclognomic®,” &c, ; “ De Naturae divinis 
Charac'erismis, seu Cosmoeritico and 
“ De Prodigiosa "Specie Naturaque Co- 
met®, ’’occasioned by the extraordinary new 
star in the constellation Cassiopeia, in 1572, 
which disappeared after being visible for 
eighteen months ; and other pieces. 
Gemma, in botany, a bud, a compendium 
ofa plant seated upon the stem and branches, 
G EM 
and covered with scales, in order to defend 
the tender rudiments inclosed, from cold 
and other external injuries, till their parts 
being unfolded, they acquire strength, and 
render any further protection unnecessary'. 
Buds, together with bulbs, which are a spe- 
cies of buds generally seated upon or near 
the root ; constitute that part of the herb 
by Linnmus called hybernacula ; that is, 
the winter quarters of the future vegetable, 
as it is during that severe season that the 
tender rudiments are protected in the man- 
ner just mentioned. Plants considered in 
analogy to animals, may properly enough 
be reckoned both viviparous and ovipa- 
rous. Seeds are the vegetable eggs ; buds, 
living foetuses, or infant plants, which renew 
the species as certainly as the seed. In ge- 
neral, we may distinguish three kinds of 
buds : that containing the flower, that 
containing the leaves, and that containing 
both flower and leaves. The first, contains 
the rudiments of one or several flowers 
folded over one another, and surrounded 
with, scales. In several trees, this kind of 
bud is commonly found at the extremity of 
certain small branches which are shorter, 
rougher, and less garnished with leaves than 
the rest. The external scales of this spe- 
cies of bud are harder than the internal ; 
both are furnished with hairs, and in gene- 
ral more swelled than those of the second 
sort. The bud containing the flower, too, 
is commonly thicker, shorter, almost square, 
less uniform, and less pointed, being gene- 
rally terminated obtusely. The second spe- 
cies of bud, contains the rudiments of seve- 
ral leaves which are variously folded over 
one another, and outwardly surrounded by 
scales, from which the small stijoul® that are 
seated at the foot of the young branches, 
are chiefly produced. These buds are 
commonly more pointed than the former 
sort. In the hazel-nut, however, they are 
perfectly round ; and in horse-ehesnut very 
thick. The third sort of bud is smaller than 
either of the preceding, and produces both 
flowers and leaves, though not always in the 
same manner. Sometimes the flowers and 
leaves are unfolded at the same time. This 
mode of the flower and leaf-bud admits of 
the following distinctions from the sex of 
the flowers so produced with the leaves : 
male flower and leaf-buds as in the pine 
and fir-tree ; female flower and leaf-buds, 
as in hazel-nut and horn-beam ; hermaphro- 
dite flower and leaf-buds, as in the elm-tree, 
cornel-tree, mezereon, and almond tree. 
GEMS, certain stones, which, on account 
