Elements of Structural and Systematic Botany

g?

tion from the lowest to the highest as to make it impracticable to make more than one sub-kingdom to include them. They are nearly all aquatic forms, although many of t

ence of a brown or red pigment. They are ordinarily divided into three classes-I. The

I.-Gre

nt in sluggish or stagnant fresh water, being much less common in salt water. They are for the most

I. Green slimes (Protococcace?); II. Confervace?; III. Pond

.-Proto

or on the damp surfaces of stones, tree trunks, etc. The plants sometimes grow

A, C), which forms a dark green slimy coating over stones, tree trunks, flower pots, e

cell division. In C iv, the young cells have mostly become free. D, a full-grown colony of Pediastrum. E, a young colony still surrounded

g size, which may in places be found to be united into groups. With a higher power, each cell (Fig. 11, A) is seen to have a distinct cell wall, within which is colorless protoplasm. Careful examination shows that the chlorophyll is confined to several roundish bodies that are not usually in imme

all is formed across the cell, dividing it into two cells, which may separate immediately or may remain united until they have undergone further division. In this

r of small cells are formed within the old one. These develop cell walls, and escape by the breaking of the old cell wall, which is left

shall see, is found in most pl

re for the most part destitute of a firm cell wall, but are imbedded in masses of gelatinous substance like many Cyanophyce?. The chloropl

lls are surrounded by a colorless gelatinous envelope. A, motionless ce

he cells escape from the gelatinous envelope, and swim actively by means of two cilia at the colorless end (Fig. 12, B). In this stage t

es of definite form. Among the most striking are the different species of Pediastrum (Fig. 11, D, E), often met with in company with other alg?, an

e outer ones being generally p

ny. The young cells now escape through a cleft in the wall of the mother cell, but are still surrounded by a delicate membrane (Fig. 11,

of a hollow net, the spaces being surrounded by long cylindrical cells placed end to end. Oth

I.-Conf

h closely, especially in their younger stages, the Protococcace?. Indeed, some of

running water, where it forms tufts, sometimes a metre or more in length. By floating ou

iven off, which may in turn branch, giving rise to a complicated branching system. These branches begin as little protuberances of the cell wall at the top of th

close together as to make the protoplasm appear almost uniformly green. Within the chloroplasts are globular, glistening bodies, called "pyrenoids." The cell has several nuclei, but they are scarcely evident in the living cell. By placing the

cid, and stained with alum cochineal. n, nucleus. py. pyrenoid, × 150. C, three stages in th

the cell wall, projecting inward, and pushing in the protoplasm as it grows. The process is continued until the ring closes in the middle, cutting the protoplasmic body completely in two, and forms a firm membrane across t

o?spores) (Fig. 13, D), which escape and swim about actively for a time, and afterwards become invested with a cell wall, and grow into a new filament. These cells

s like Stigeoclonium (Fig. 14, A), Ch?tophora and Draparnaldia (Fig. 14, B, C), very much branched. The two la

aparnaldia, × 50. C, a piece of Draparnaldia,

lettuce (Ulva), shown in Figure 15. The thin, bright-green, lea

sea lettuce (Ulva).

us species of ?dogonium and its relatives. There are numerous species of ?dogonium not uncommon in stagnant water growing

Even when not fruiting the filaments may usually be recognized by peculiar cap-shaped structures at the top of some of the cells.

he zo?spore comes to rest, secretes a cell wall about itself, and the transparent end becomes flattened out into a disc (E, d), by which it fastens itself to some object in the water. The upper part now rapidly elongates, and dividing repeatedly by cross walls, develops into a

a small male plant with an antheridium (an.). C, a zo?spore of ?dogonium. D, a similar spore germinating. E, base of a filament showing the disc (d

in form (Fig. 16, A, B). When fully grown, the contents contract and form a naked cell, which sometimes shows a clear area at one point on the surface. This globular mass of protoplas

formed, and enter the o?gonium. By careful observation the student may possibly be able to follow the spermatozoid into the o?gonium, where it enters the egg cell at the clear spot on its surface. As a result of the entrance of the spermatozoid (fertilization), the egg cell becomes surrounded by a thick brown wall, and becomes a resting

, × 50. B, a few cells from the

genus Bulboch?te, characterized also by hairs swollen at th

riking resemblances to the red seaweeds, and possibly form a transition from the green alg? to the red. The commonest species form bright-green discs, adhering firml

base, including a very long and delicate filament (Fig. 17, B). In their methods of