("7) 



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 of 

 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 



