Imágenes de páginas

Oidium conidium formations have been observed by Brefeld in many mushroom fungi (Agaricinec). Some botanists are therefore of the opinion that Didium lactis is really a stage of development of such fungi. Proof of this has not yet been advanced.

Dematium pullulans, de Bary. The fungus (Figs. 129, 130, 131 and 132) designated by this name has a branched, colourless mycelium on the surface of which, apparently without order, it frequently produces yeast cells or conidia by budding; the latter are mostly oval. These yeast cells are often situated on the

[merged small][ocr errors][ocr errors]

threads on small humps which are sometimes discernible after the release of the yeast cells. They can then either produce more yeast cells by budding or develop germ threads, which grow into mycelia. Swollen parts are frequently found in the mycelium, which, after a certain time, become thick-walled and dark coloured, usually greenish-brown; the single cells developed by budding may also undergo transformation in this way. Gemmæ, which, among other ways, can be recognised by their contents (large oil and fat drops), are thus formed. Dematium pullulans does not induce fermentation. Fig. 130 represents an inter-growth similar to that which has been described under Botrytis and Oidium. Such endogenous conidia have been regarded and described as endospores. The author has shown, however, in con




Fic. 128.- Oidium lactis, Fresenius. Phenomenon of inter-growth. 499.

(After Klöcker and Schiönning.)

junction with Schiönning, that in these cases it is a matter of inter-growth only. The phenomenon is brought about when a vigorous mycelium cell in the immediate neighbourhood of a feebler cell acts as a parasite on the

[ocr errors]

FIG. 129.—Dematium pullulans, de Bary. I, A chain of gemmæ ; three mem

bers of this (a, b, c) have produced mycelium tubes (mn) on which conidia (at d) are developed. II, A chain of gemmæ developing conidia directly (at d). III, A conidium a, which has grown & mycelium thread m, on which conidia are formed ; it has also formed conidia directly. IV, Conidium divided into two cells under similar conditions. V, Conidium divided into two cells developing conidia. VI, a-9, Continuous development of one and the same gemma, in a very shallow water layer with free air supply, into a double-celled, thick-walled, brown gemma rich in fat. VII and VIII, Mycelia divided up into simple, short, swollen members, which have become thick-walled gemmæ, generally much browned and furnished with large oil drops. At VIII a some of the gemmæ are seen still further divided by septa, which lie in the same direction as the axis of the thread. 549. (From Zopf's handbook.)

20 *


Fig. 130.- Dematium pullulans, de Bary. Phenomenon of inter-growth. a and latter, and forms chains of yeast conidia at the end next to, and within the feebler cell; or, less frequently, the vigorous cell injects a longer or shorter mycelium thread (Fig. 130 a, b, e and g). The yeast conidia formed in the interior of the cell may further increase here by budding

b show intruded mycelium threads, in b the thread is forming conidia. Conidia are being abstricted on both sides. d, A conidium in the act of budding. e, A mycelium thread has grown through the septa of two cells into a cell filled with conidia. f, Cell with four conidia strongly resembling endospores. 9, One of the cells has developed conidia, a mycelium thread has grown in from the other. The remaining figures show various examples of endogenous conidium formation. e was observed at about 20° C. in a water culture about one month old ; the remainder were observed in water cultures two days old at 20° and 25° C. 209. (After Klocker and Schiönning.)

[merged small][merged small][merged small][merged small][ocr errors][ocr errors][merged small][merged small][ocr errors][ocr errors][merged small]

b Fig. 131.- Dematium pullulans, de Bary. Two development series of endo

genous conidium formations directly observed in cover glass water cultures. In the series a the development proceeded for five hours, and in b for twenty. four hours at 20° C. 409. (After Klöcker and Schiönning.)

(Fig. 130 d), while the intrusive mycelium thread forms conidia (Fig. 130 b). When a weak cell lies between two vigorous ones, both of these latter can grow into the feeble one and form chains of yeast conidia (Fig. 131 a,-a,), or one cell intrudes a mycelium thread, while the other simply

« AnteriorContinuar »