(117) 
plants. This extensive group seems to have followed two 
independent lines of development and consequently the 
plants fall into two well-marked groups, the first being 
the gymnosperms, cone-bearing plants, or plants in which 
the seeds are borne exposed in variously shaped cones 
(cases 56 to 58). This is a comparatively small group, 
but exhibits great diversity, including plants ranging from 
straggling shrubs or vines to the largest trees. The leaves, 
too, vary from structures resembling needles or scales to 
expanded fern-like structures of considerable variety’ 
In a former geological age these plants were the dominant 
seed-bearing plants, but now the second group of the sper- 
matophytes largely predominates; namely, the angio- 
sperms, covered-seeded plants in which the seed is borne 
in a seed-case. These plants also existed in the later 
geological ages, and now form the most important and 
conspicuous part of the vegetation of the earth. The 
covered-seeded plants (cases 59 to 128) fall into two divi- 
sions, the one in which the embryo has a single leaf, the 
monocotyledons (cases 59 to 71); the other in which the 
embryo has two leaves, the dicotyledons (cases 72 to 128). 
(b) Microscope Exhibit. The exhibition microscopes 
occupy small stands on the mezzanine landing between the 
first floor and the second floor. In front of the windows 
on the right, if one enters by the right stairway, are shown 
a few of the simplest and smallest forms of plant life. 
Under the lenses of the first microscope are representa- 
tives of the diatoms—one-celled organisms, some o 
which have the power of animal-like locomotion; the 
living substance of each cell is enclosed and protected by a 
hard transparent glassy wall consisting of two halves, 
one of which fits into the other like a band-box into its 
cover. The second microscope shows attractive and 
varied forms of fossil diatoms from California. Following 
this are shown “‘sea mosses,” or “‘seaweeds,” as they are 
commonly known, and closely related minute plants which 
inhabit fresh water and belong to groups often referred to 
