. The fungi which cause plant disease . Plant diseases; Fungi. 78 THE FUNGI WHICH CAUSE PLANT DISEASE strictly parasitic habit. The myceUal threads in most genera wander between the host cells and draw nutriment from them by short branches, sucking organs (haustoria), (Fig. 49) of various forms, which penetrate into the victimized cell. In one genus only, Phytophthora, does the mycelium grow directly through cells. Two kinds of spores are produced, sexual and asexual. The sexual spores result from the union of two unlike gametes, the egg (oosphere) and sperm, borne respectively in the oogonium
. The fungi which cause plant disease . Plant diseases; Fungi. 78 THE FUNGI WHICH CAUSE PLANT DISEASE strictly parasitic habit. The myceUal threads in most genera wander between the host cells and draw nutriment from them by short branches, sucking organs (haustoria), (Fig. 49) of various forms, which penetrate into the victimized cell. In one genus only, Phytophthora, does the mycelium grow directly through cells. Two kinds of spores are produced, sexual and asexual. The sexual spores result from the union of two unlike gametes, the egg (oosphere) and sperm, borne respectively in the oogonium and antheridium. Each oogonium bears a solitary oosphere. Fertilization is accom- plished by means of a tube from the anther- idium and penetrating into the oogonium. The sexual spores are thick walled, re- FiG. 49.—^Haustoria of a . , , ,, . , ,. Peronospora. After sistant, and usually require a long time to ^°'*^" reach maturity. They are, therefore, often called "resting ; In germinating the sexual spores pro- duce either germ tubes or develop directly into zoosporangia. The asexual spores are conidia. They are borne on conidio- phores which arise from the mycelium and which may be short or long, simple or branched, subepidermal or superficial accord- ing to the habit of the species. The conidia in various genera germinate by three methods, (1) a germ tube is sent out by the conidium, (2) the entire protoplasmic contents of the spore passes outside the spore wall and then forms a germ tube, or (3) the conidium by internal division breaks up into zoospores. Key to Families of Peronosporales Conidiophores, short, thick, subepidermal, conidia catenulate 1. Albuginaces, p. 78. Conidiophores, longer, superficial, simple or branched, conidia not catenulate 2. PeTonosporaces, p. 82. Albuginacese There is a single genus. Albugo (Persoon) Roussell. This genus of about fifteen species is entirely parasitic upon flowering Please note that these images
Size: 1695px × 1475px
Photo credit: © Central Historic Books / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, booksubjectfungi, bookyear1913
