and putting into this drop of water the spores whose germination it is desired to watch; as, however, the spores do not germinate for several hours, the drop of water would evaporate, unless means be taken to prevent it, before the germination takes place. This is easily done by placing the glass slide under a bell-glass, inverted over a plate of water, so that it is kept continuously in a saturated atmosphere. Any suitable object will do to place the slide on; but the most convenient appliance will be found to be a simple stand or rack (Fig. 9), which can be constructed

in a few minutes out of two flat pieces of gutta-percha and four glass rods. The gutta-percha which is used for soling boots answers well enough. If two oblong pieces of equal size, say three and a half by four and a half inches (9 X 12 cm.), be taken, and a hole bored at each of the four corners, and through each pair of holes let a glass rod be passed, a very simple stand is made at the cost of a few pence. For the glass rods an old barometer tube, cut into suitable lengths with a file, does well enough. The great advantage of such a stand is, that when the slides are laid across the rods, they touch only at two

points, so that when placed under the microscope there is no necessity to wipe the lower side of the slide. Of course, the length and height of the stand must be proportionate to the size of the bell-glass. The best form of bellglass is that known by gardeners as a propagating glass, which is rather flatter than the ordinary bell-glasses; the advantage being that the slides are not too far above the surface of the water in the plate, so that the drops of water on them do not evaporate so rapidly.

Supposing we wish to observe the germination of the æcidiospores of Puccinia graminis, having obtained a perfectly fresh-gathered leaf of barberry with the Æcidium on it, we proceed as follows. The spores can either be brushed upon the slide with a camel-hair pencil, or what will often be found more convenient, the acidium can be gently struck upon the dry slide, and a drop of water let fall upon the tiny heap of golden spores that have been displaced. The ripe spores will most of them float on the top of the water and can be readily observed with a quarter-inch objective. The preparation must, of course, not be covered with a cover-glass, and it takes a little patience to examine these uncovered objects, because the front of the object-glass is apt to become bedewed and misty. The only plan is to raise it by the coarse adjustment, wipe it dry, and try again.

Germination will be well advanced in the course of ten or twelve hours, and the migration of the yellow endochrome along the germ-tube will by that time have taken place. This will be followed by their circumnutatory movements and ultimate branching. Earlier examination of the preparation will show the germ-tubes emerging from the germ-pores. It is useless to attempt to get æcidiospores to germinate unless they are perfectly fresh and perfectly ripe. For instance, the spores dug out from the bottom of an æcidial cup with a needle will not germinate;

nor will they if they have once become thoroughly dry. The same method is to be adopted with the uredospores, and the same precautions observed. With regard to the teleutospores, certain modifications of the above are necessary. If one of the Leptopucciniæ is to be examined, all that is requisite is to cut up one of the sori and place the fragments in a drop of water, and in a few hours the promycelia will be developed. Those species which have a prolonged period of rest in their life-history, it is, of course, useless to attempt to germinate except at the proper season of the year. Suppose it is desired to observe the germination of P. graminis, in the autumn some specimens of mildewed straw must be procured, and preserved through the winter. I have always found the best plan is to tie them up in a bundle and keep them out-of-doors, so that they are exposed to the same vicissitudes of temperature and moisture as would happen to them in a state of nature; for it is obvious that if they be kept throughout the winter indoors, they will not only be maintained at a higher temperature, but also will become more completely dried than is natural to them. Under such circumstances they neither germinate so freely nor so uniformly as they do when they have passed the winter in the open air. Specimens of P. graminis may be obtained on Triticum repens, in February or March, from the immediate vicinity of any barberry bush, and these will be found to germinate. very readily. Having obtained the material, in March or April, however it may have been preserved, in order to get it to germinate all that is required is to place it in water. If some of the spore-beds be cut into pieces about oneeighth of an inch (2 or 3 mm.) across, and placed in water in a watch-glass, under the bell-glass, the process of germination soon commences, perhaps in twelve hours, perhaps longer, according to the manner in which the material has

been preserved, and according to the temperature of the atmosphere at the time the experiment is made. I never remember having seen any teleutospore germinate if the temperature within the bell-glass was below 5° C. Germination is very partial and very slow at 8° C., but at from 10° to 15° C. it is both vigorous and rapid. The germination can be recognized to have taken place, if it be at all free, by the naked eye; the clusters of spores will then be seen to be surrounded by an opalescent, hazy cloud, which, when placed under the microscope, will be found to consist of myriads of promycelia. A very convenient method of preserving material on grasses-such, for instance, as Uromyces poæ, which occurs on the leaves of the grass that in the ordinary course of events become disintegrated by decay during the winter-is to gather a small bundle of affected leaves, attached to the stems, place this bundle in a flower-pot just as if it were a living plant, to cover the flower-pot with a bell-glass, and keep it out-of-doors in a shady place all winter. There will be enough moisture in the atmosphere to prevent the material from being injured by desiccation, but not enough to allow the teleutospores to germinate until they are purposely placed in water. The bell-glass will protect the grass from injury by wind and weather; so that when spring comes you will have abundance of material ready to hand, in excellent condition for germination, which you can induce at pleasure, by merely soaking it in water. The same method may be conveniently adopted with those species which occur on leaves, and in which the spores are lost by their decay in the ordinary course of events. The Melampsora on willow and poplar may thus be kept out-of-doors under a bellglass with great facility.

With those species which occur on leaves of plants which have a very perishable foliage, it is necessary to

collect specimens which are perfectly mature, if possible, upon leaves that are beginning to fade from age, and dry them in the ordinary way between blotting-paper. When the spring comes, the affected leaves must be soaked for twenty-four hours in water, and the spores examined to see if any attempt at germination is observable. If not, the soaked leaves may be wrapped in an old, well-washed piece of calico, and buried for a day or two in the ground; after which treatment, a few spores must be tried in a drop of water on a glass slide. Should they fail to evince any signs of vitality, the leaves must again be buried for a day or two longer, and re-examined.

The entrance of the germ-tube into the host-plant can be observed in various ways. The promycelial spores can be applied to the surface of a leaf, and sections made a few hours afterwards. This is, however, an exceedingly delicate process, and requires not only patience, but considerable manipulative skill. A piece of the epidermis may be stripped off and laid flat upon a moistened slide, and the spores placed on it; if the preparation be kept in a moist. atmosphere for a few hours, the germ-tubes can be seen boring through the cells. Another plan is to place a mass of teleutospores, which has first been seen by the microscope to be in active germination, on a leaf, and to keep it for a few hours under a bell-glass in a moist atmosphere. The teleutospore mass can be seen by the naked eye, and is a guide to the exact part of the leaf to be examined. By a little deft manœuvring, pieces of the epidermis at this spot can be ripped off with the point of a penknife, and examined either on their external or internal surfaces. By similar methods, the entrance of the uredospore and æcidiospore germ-tubes can be observed, only, being larger and containing yellow endochrome, the process is less difficult. With most of the Ustilagineæ, all that is necessary is to