Elements of Structural and Systematic Botany

ng

ic matter for food, some being parasites (growing upon living organisms), others saprophytes (feeding on dead matter). Some of them show close resemblances in structure to certain alg?, and there is reason to believe that they are descended from forms that originally had

.-Phyco

hose of Vaucheria or other Siphone?, but always destitute of any trace of chlorophyll. The simplest of these

rs or so it will be covered with a film of fine white threads, and a little later will produce a crop of little globular bodies m

n the atmosphere falling on the bread, which offers the

int to another. As it grows it sends out these runners along the surface of the bread, or even along the inner surface of the glass covering it. They fast

ter). After carefully spreading out the specimens in this mixture, allow a drop of alcohol to fall upon the preparation,

the growing tips of the branches. The spore cases, "sporangia," arise at the ends of upright branches (Fig. 32, C), which at first are cylindrical (a), but later enlarge at the end (b), and become cut off by a convex wall (c). This wall pushes up into the young sporangium, forming a structure called the "columella." When fully grown, the sporangium is globular, and

s (Fig. 32, E) are set free. The columella remains unchanged,

v, × 50. D, spore case which has discharged its spores. E, spores, × 300. F, a form of Mucor mucedo, with small accessory spore cases

scums are also known, but only occur after the plants have gr

k of the sporangium, which is also smaller, and in not forming runners. This species sometimes bears clusters of very small

met with, parasitic upon

mmonest of these attacks the house flies in autumn, when the flies, thus infested, may often be found stick

Rusts and Mildew

grow within the tissues of various flowerin

rantus). It forms whitish, blister-like blotches about the size of a pin head on the leaves and stems, being commonest on the under side of the leaves (

s of the leaf, and have pushed it up by their growth. If the section is a very thin one, we may be able to make out the structure of the fungus, and then find it to be composed of irregular, tubular, much-branch

ng up and becoming constricted, so as to form an oval spore, which is then cut off by a wall. The portion of the filament immediately below acts in the same way, and the process is repeat

out of the water. After about twenty-four hours, if some of the spores are scraped off and mounted in water, they will germinate in the course of an hour or so. The contents divide into about eight parts, which escape from the top of the spore, which at this time p

?spores. E, germinating zo?spores. sp. the spore. F, young. G, mature sexual organs. In G, the tube may be seen connecting the antheridium (an.), with the eg

t, and the filaments enter the plant through the breathing pores on the lowe

must be freed from the host plant. In order to do this, small pieces of the leaf should be boiled for about a minute in strong caustic potash, and then treated with acetic or hydrochloric aci

which arises as a swelling of one of the filaments, and becomes shut off by a wall. At first (Fig. 33, F) its contents are granular, and fill it completely, but later

with the o?gonium, may be detected (Fig. 33, F, G, an.), and in exceptionally favorable cases a t

ark-colored on the outside, and showing a division into several layers, the outermost of which is dark brown, and

the white rust of the shepherd's-pu

rm cell may develop into a spore without being fer

s of the vine mildew (Per

ttacks shepherd's-purse, radish, and others of the mustard family, upon which it for

s through the stem showing very beautifully the structure of the fungus,

nospora, Phytophthora). These plants form mouldy-looking patches on the leaves and stems of many plants, and are often very destru

prolegniace?

ey may usually be had for study by throwing into water taken from a stagnant pond or aquarium, a dead fly or some other insect. After a few days it will probably be found covered with a dense growth

zo?sporangium, × 100. C, the same discharging the spores. D, active. E, germinating zo?spores, × 300. F, a second sporangiu

those of Vaucheria, but entirely destitute of chlorophyll. In places these filaments are filled with densely granular protoplasm, which

e first sign of division is the appearance in the protoplasm of delicate lines dividing it into numerous polygonal areas which soon become more distinct, and are seen to be distinct cells whose outlines remain more or less angular on account of the mutual pressure. When ripe, the end of the sporangium opens, and the contained cells are discharged (Fig. 36, C). In case they have no membrane, they swim away at once, each being provided with two cilia, and

ing up through it (Fig. 36, F) and the end being again cut off, or else by a branch bu

usually after the formation of zo?spores has ceased; but in many cases, perhaps all, these develop without being fertilize

as do the sporangia, from which they differ at this stage in being of globular form. The contents contr