246 THALLOPHYTES. 



Zygospore), which then increases (to i mm.) and takes the form of a sphere flattened 

 by the two supporting-cells. The exospore is thick and of a blue-black colour. The 

 formation of zygospores takes place in May, June, and July, on stone-fruit and berries, 

 and takes twenty-four hours for its completion. The germination of the zygospores has 

 been observed in another genus, Sporidinia grandis {Mucor Syzygites), which infests fleshy 

 Fungi. In this case tBiey form a filament, on which is developed a system of sporangia 

 with asexual spores ; these then produce a mycehum which forms first zygospores and 

 then again asexual spores. An alternation of generations thus takes place ^. 



II. The Hypodermic 2^ The best known species of this order, Puccinla graminis, 

 belonging to the family Uredineae, may be taken as its type. Its development not only 

 shows a distinct alternation of generations (although no sexual organs are as yet known), 

 but also in combination with it, the hetercecism which occurs also in some other Fungi, 

 but is not elsewhere so clearly defined. De Bary has given the term Hetercecism to that 

 peculiarity by which one generation of a parasitic Fungus is developed exclusively on 

 one host, or only on those which belong to a particular group, while another stage of 

 development of the same species occurs only upon a different host. 



On the leaves of BerberLs 'vulgaris are found in the spring yellowish swollen spots, 

 where dense masses of mycelial filaments are interposed between the parenchyma-cells 

 (Fig. 170, ^ and /, the felted mycelium, lying between the cells, being indicated by 

 dots). In these swollen spots are found two kinds of fructification, the Spermogonia, 

 which are produced somewhat earlier, and the j^cidia. The spermogonia (Fig. 170, J, j/») 

 are urn-shaped receptacles surrounded by a layer of mycelium as by an envelope ; 

 hair-like threads which clothe the cavity protrude in the form of a brush from the 

 opening of the spermogonium, penetrating the epidermis of the leaf; the bottom of the 

 spermogonium is covered with short mycelial branches, from the ends of which are 

 detached numerous very small spore-like bodies, the Spermatia. The second form of 



^ [On the Mucorini, the Memoirs of Brefeld (Botanische Untersuchungen iiber Schimmelpiize, 

 Leipzig 1872), and Van Tieghem and Le Monnier (Ann. des Sci. Nat. 1873, vol. XVII, and Quart. 

 Journ. Micr. Sc. 1871, pp. 49-76), should be consulted. The following particulars are extracted 

 from the last cited memoir. The mycelium of the Mucorini always originates from an asexual 

 spore. The zygospores never give rise in germinating to a mycelium, but always produce, as in other 

 Fungi, and as also in Muscineae, an asexual reproductive apparatus. The mycelium is at first always 

 destitute of partitions ; later, as the protoplasm disappears, septa make their appearance irregularly. 

 The filaments occasionally anastomose ; they may be wholly immersed in the nutrient medium or 

 partly aerial. The mycelium of some species {e. g. Chaetocladium), which are normally nonpara- 

 sitic, have also the capacity of fixing themselves on the mycelium of other species and living para- 

 sitically. All the Mucorini develope sporangia upon aerial extensions of their mycelium, in which 

 asexual spores originate by division of the protoplasm. In some genera {e. g. Thamnidium) these 

 sporangia are of two kinds, but the spores they contain are similar. Peculiar asexual spores (Chlaray- 

 dospores) also arise by local condensation of the protoplasm within the mycelium and in different 

 positions. A single large echinulate or tuberculate chlamydospore may be formed within the extre- 

 mities of all the branches of the aerial hyphae ; and this may for a long time be the only mode of 

 reproduction exhibited (Mortierella). Zygospores arise from a true conjugation. They have been 

 observed in six genera : Sporodinia (Ehrenberg, 1829), Rhizopus (De Bary, 1866), Mucor {M.ftisiger, 

 Tulasne, 1866, M. Mticedo, Van Tieghem and Le Monnier, Comptes Rendus, Apr. 8, 1872), Phyco- 

 myces (Van Tieghem and Le Monnier, 1872), Cha^tocladium and Piptocephalis (Brefeld, 1872). 

 Before germination the zygospore requires a certain period of dryness and rest. After again becom- 

 ing moist it pro<luces without mycelium a system of sporangia having all the characters of those 

 which the mycelium produces. — Ed.] 



'' De Bary, in Monatsber. der k5nigl. Akad. der Wissen. in Berlin, Jan. 12, 1865.— Ditto, 

 Recherches sur k Developpement de quelques Champignons para-sites : Annales des Sci. Nat. 4th 

 series, vol. XX, Div. i.— Rees, Die Rostpilze der deutschen Coniferen. Halle 1809. 



