90 



KNOWLEDGE. 



[ArRii. 1, 1897. 



Pthi/tisma have also a carbonized rind, but they differ from 

 those of Sphceria iu forming a confluent mass which opens 

 by flexuous fissures. The flattened sporocarps are closely 

 applied to the upper surface of the sycamore leaf, and 

 within the black rind is a mass of soft, thin-walled tissue, 

 in the upper part of which, with the aid of the microscope, 

 the asci may be distinguished (Fig. III. 1). 



On a much larger scale we have in the truffle a body of 

 essentially the same nature. Esteemed by epicures a 

 vegetable delicacy, the truffle is the underground sporocarp 



FiO. III. — 1. Section of Sycamore Leaf with Sporocarps oi Shviisma. 

 2. Grass Blade with Spharice, i. Section of Grass Blade mth 

 t^porocarps of Spharia. 



of an ascomycetous fungus. It has somewhat the appear- 

 ance of a potato with a rough warted exterior. The solid 

 substance inside shows marbled veins ; under the micro- 

 scope the white areas are seen to consist of ordinary 

 mycelial tissue ; the darker veins are masses of rounded 

 asci, each enclosing two, four, or eight ascospores. In this 

 country truffles rarely exceed three or four ounces, but in 

 Italy and Germany they frequently attain a weight of 

 several pounds. The people of those districts from which 

 the principal supplies come employ pigs and specially 

 trained dogs to guide them to the spots where the truffles 

 lie buried, and in this way discover where to dig for them. 

 The species of Tuber are fairly numerous (Fig. IV. 1). 



If we imagine a minute truffle with its tubers flattened 

 out into thin hollow plates, and these glued to the upper 

 surface of the leaf, we have a fairly correct notion of the 

 nature of the Bhi/tiswa spots on the sycamore. 



The sporocarps of Sphieria and Rlii/tisma grow directly 

 from the mycelium ; in other Ascomijcetes the mycelium 

 develops a hard, rounded, tuber-like sclerotium, containing 

 reserve material, from which sporocarps are afterwards 

 formed. Some part of the mycehum very generally 

 assumes a sclerotioid and carbonized character as a 

 preliminary to the formation of asci. Sclerotia may 

 become detached and be dispersed : they usually remain 

 dormant for a time ; as little horny bodies they are fre- 

 quent on the grams of grasses, rushes, and sedges ; several 

 kinds occur attached to the bodies of insects. Ergot 

 grains are the sclerotia of Claviceps : in this case the 

 sporocarps are not formed in the sclerotium, but from the 

 latter there arise stalked club-like organs called stromata, 

 and the perithecia containing asci are developed in the 

 substance of the stroma (Fig. IV., 3 and 1). 



The stroma forms the most conspicuous part of the 

 fungus iu the Xylariw, common on old tree stumps ; their 

 erect branching stromata might be compared to little 

 pieces of blackened coral. They are covered with a layer 

 of cells bearing white gonidia, but when these are .shed 

 the carbonaceous rind beneath is exposed ; it encloses 

 softer tissue in which perithecia are formed. Each peri- 

 thecium communicates with the exterior through a small 



opening in the rind ; these openings have a lining of hairs 

 which assist in discharging the ascospores. Much, then, as 

 the little twig-like Xylaria (Fig. IV. 5), the truffle, and 

 the wafer-like sporocarps of lilnjtisma difl'er in external 

 form, they are only different modifications of the same 

 type of structure. 



In those Ascomycetes which have been fully investi- 

 gated, the sporocarp and asci are found to be the pro- 

 duct of fertilization. The rose-blight fungus is one of 

 the simplest ; its web-like mycelium, which spreads over 

 the leaves of its host, develops specialized cells, the antheri- 

 dium and carpogonium, functionally equivalent to the 

 stamens and pistils of flowering plants. After fertilization 

 the carpogonium divides into two cells, one of which 

 becomes an ascus with eight ascospores. From a cell 

 beneath it filaments arise, which closely invest the ascus 

 and constitute the wall of the little spherical sporocarp. 

 The development of Krysiphe is very similar ; the 

 carpogonium is more highly differentiated in the bread 

 mould Eurotiuw, and in Pezha it is provided with an 

 additional style-like organ, the trichogyne, to which the 

 antheridium is applied in fertilization. The common 

 cheese mould is a small truffle ; its minute sporocarps, 

 no larger than grains of sand, result from a process of 

 fertilization similar to that of F.rysiphe and Eurotium. 

 The formation of asci appears to depend on sexual repro- 

 duction, and though not yet proved in every case the view 

 is commonly held by mycologists that fertilization is uni- 

 versal among the Ascomycetes. 



The sporocarps of certain species are extremely rare, 

 the fruits of some being quite unknown. The Erysiphe of 

 the grape vine, notwithstanding its wide diffusion over 

 Southern Europe, has never i^een known to produce a 

 sporocarp. Its propagation is effected entirely by gonidia, 

 as those reproductive cells are termed which do not result 

 from fertilization, but are formed by simple vegetative 

 division. On most species both sporocarps and gonidia 

 occur, but the latter are usually much more abundant. A 

 mildew (Erysiphe yraminis) forms httle white flocculent 

 tufts, very common on the blades of many grasses in 

 autumn ; these are made up of strings of egg-shaped 

 gonidia (Fig. V. 1). Another species attacks fruit trees. 

 A pear tree we examined looked as though it had been all 

 powdered over with chalk. On submitting a portion of 

 a leaf to the microscope, there was seen projecting from 

 the epidermis a perfect forest of crystalline gonidia chains, 

 as beautiful a microscopic object as one could wish. Yeast 

 has some claim to be regarded as the gonidial condition of 



Fm. IV.— 1. Truffle. 2. Its Ascus. 3. Ergot;— .sc. Sclerotium, 

 6^ Stroma. 4. Section of Stroma, showing Perithecia. 5. Xi/laria. 



an Ascomycete. Ordinarily it is propagated in saccharine 

 solutions by budding, but if nutriment be deficient, as 

 when it is grown on a slab of plaster of Paris, many of the 

 cells assume the appearance of asci, each producing four 

 spores in its interior. Gonidia are of various forms ; the 

 same mycelium may bear two or three different kinds, as in 

 the Uiedincs, where the teluto and uredospores are non- 

 sexual spores or gonidia. In the common moulds 

 Eurotium and Pcnieitliiim, the gonidia chains are formed 

 in clusters at the top of a slender stalk, giving the fructi- 



