Part 7 (2/2)

There are twoonly a few forms, most of which are not likely to be met with by the student

In these the spore sacs are borne directly upon the fila The only forus (_Exoascus_) that attacks peach-trees, causing the disease of the leaves known as ”curl”

All of the co to the second division, and have the spore sacs contained in special structures called spore fruits, that may reach a diah ordinarily roup are theupon the leaves and ste serious injury by their depredations They forrayish downy fil like hoar-frost Being very common, they may be readily obtained, and are easily studied One of the best species for study (_Podosphaera_) grows abundantly on the leaves of the dandelion, especially when the plants are growing under unfavorable conditions The same species is also found on other plants of the sa the su, the spore fruits material should be collected in late summer or early autu dingier as it becomes older, and careful scrutiny of the older specimens will show numerous brown or blackish specks scattered over the patches These are the spore fruits

[Illustration: FIG 39--_A_, spore-bearing filaer spore, 150 _C-F_, development of the spore fruit, 300 _ar_ archicarp _G_, a ripe spore fruit, 150 _H_, the spore sac re fila the enlargee, 300 _K_, spores, 300]

For microscopical study, fresh material may be used, or, if necessary, dried speci, should be soaked for a short time in water, to which has been added a few drops of caustic-potash solution This will remove the brittleness, and swell up the dried filainal proportions A portion of the plant should be carefully scraped off the leaf on which it is growing, thoroughly washed in pure water, and transferred to a drop of water or very dilute glycerine, in which it should be carefully spread out with needles If air bubbles interfere with the examination, they lass put on If the specilycerine, it will keep indefinitely, if care is taken to seal it up The plant consists of much-interlaced filaments, divided at intervals by cross-walls[6] They are nearly colorless, and the contents are not conspicuous These fila 39, _A_), that become divided into a series of short cells by means of cross-walls The cells thus fore out at the sides, beco broadly oval, and finally becoive the frosty appearance to the early stages of the fungus when seen with the naked eye The spores fall off very easily when ripe, and gerrow into fila 39, _B_)

[6] The filaments are attached to the surface of the leaf by suckers, which are not so readily seen in this species as in soarden chrysanthemum, however, shows them very satisfactorily if a bit of the epiderrow is sliced off with a sharp razor andthe air with alcohol These suckers are then seen to be globular bodies, penetrating the outer wall of the cell (Fig 40)

[Illustration: FIG 40--Chrysanthe the suckers (_h_) by which the filaments are attached to the leaf

_A_, surface view _B_, vertical section of the leaf, 300]

The spore fruits, as already observed, are formed toward the end of the season, and, in the species under consideration at least, appear to be the result of a sexual process The sexual organs (if they are really such) are extre to their very small size, are not easily found They arise as short branches at a point where two fila 39, _C_, _ar_), the feer than the other and nearly oval in form, and soon becomes separated by a partition frorows up in close contact with the archicarp, and like it is shut off by a partition from its filament It is more slender than the archicarp, but otherwise differs little from it No actual communication can be shown to be present between the two cells, and it is therefore still doubtful whether fertilization really takes place Shortly after these organs are full-grown, several short branches grow up about them, and soon coether, and cross-walls are for spore fruit appears surrounded by a single layer of cells, sufficiently transparent, however, to allow a view of the interior

The antheridiue, but the archicarp soon divides into two cells,--a srow fro cells, short filaments, that almost completely fill the space between the archicarp and the wall An optical section of such a stage (Fig 39, _F_) shows a double wall and the two cells of the archicarp The spore fruit now enlarges rapidly, and the outer cells beco thicker and harder as they change color Sorow out from their outer surfaces, and these are also dark-colored

Shortly before the fruit is ripe, the upper cell of the archicarp, which has increased ht parts, each of which develops a wall and beco the ripe spore fruit, these spores still enclosed in the39, _H_) These spores do not germinate at once, but remain dormant until the next year

[Illustration: FIG 41--Forms of mildews (_Erysiphe_) _A_, _Microsphaera_, a spore fruit, 150 _B_, cluster of spore sacs of the sae of _Uncinula_, 300 _E_, appendage of _Phyllactinia_, 150]

Frequently other structures, rese so 39, _I_, _K_), and were for a long tian; but they are non to belong to another fungus (_Cicinnobulus_), parasitic upon the mildew They usually appear at the base of the chains of conidia, causing the basal cell to enlarge toconidia, which shrivel up A careful examination reveals the presence of very fine filaments within those of the mildehich may be traced up to the base of the conidial branch, where the receptacle of the parasite is for The spores contained in these receptacles are very s, worm-shaped masses, if the receptacle is placed in water

The enera: _Podosphaera_, with a single ascus in the spore fruit; and _Erysiphe_, with two or more In the latter the archicarp branches, each branch bearing a spore sac (Fig 41, _B_)

The appendages growing out from the wall of the spore fruit are often very beautiful in foriven above are often subdivided according to the fores

A common mould closely allied to the mildews is found on various articles of food when allowed to remain damp, and is also very common on botanical specimens that have been poorly dried, and hence is often called ”herbarium mould” (_Eurotium herbarioru filament of the herbariu the way in which the spores are borne--optical section-- 150 _D_, spore fruit of the herbarium mould, 150 _E_, spore sac _F_, spores, 300 _G_, spore-bearing filament of the common blue mould (_Penicilliureenish color, and produced on the ends of upright branches which are enlarged at the end, and froive rise to the conidia in the sa 42, _A_)

Spore fruits much like those of the mildews are forrains (Fig 42, _D_)

These contain nuht spores

There are nu in color and size, soreen form

Another form, common everywhere on mouldy food of all kinds, as well as in other situations, is the blue eneral appearance, resembles aluishable by aall of these forms, they lycerine; but reat care, as the spores becoer _Ascoi (_Discomycetes_) may be taken as types The spore fruit in these forms is often of considerable size, and, as their na the form of a flat disc or cup A brief description of a coive an idea of their structure and development