Phylum Iiiophyta [ 139 



stroma, are assigned to order Sphaeriales. Forms with perithecia in or on a brightly 

 colored stroma are Hypocreales. Those whose perithecia are cavities with a wall 

 indistinguishable from a dark stroma are Dothideales. These groups are not confi- 

 dently acceptable as natural: the stromatic Sphaeriales (Wehmeyer, 1926), the 

 Hypocreales, and the Dothideales appear each to include more than one line of 

 descent from Sphaeriales with solitary perithecia. 



As a general rule, each perithecium develops in consequence of a separate act of 

 fertilization, of a differentiated ascogonium, either by an antheridium, a spermatium, 

 or otherwise. 



Gaumann recognized fourteen families in the present group or groups. To these 

 are to be added a great number of lichen-formers, properly Sphaeriales and Hypocre- 

 ales,. but construed as a single family Verrucariacea; and a smaller number, repre- 

 senting the Dothideales, and called Mycoporacea. 



Exmples include the following: 



Among Sphaeriales with solitary perithecia, Mycosphaerella is a genus of more 

 than one thousand parasites on plants, mostly inconspicuous, causing leaf spots. 

 Their conidia are of various types, Septoria, Phleospora, Ramularia, Cercospora. 

 Venturia, another numerous genus, includes V. inaequalis, causing apple scab; its 

 conidia are of a type called Fusicladium. 



Four species of Neurospora were discovered by Shear and Dodge (1927) as the 

 fruiting stages of a red mold on bread called Monilia sitophila. Genetic study of 

 this genus particularly by Tatum, Beadle, and their associates (Ryan, Beadle, and 

 Tatum, 1943; McClintock, 1945; Beadle and Tatum, 1945; Tatum and Bell, 1946; 

 Mitchell and Houlahan, 1946; Tatum, Barratt, Fries, and Bonner, 1950) has yielded 

 results of the highest theoretical significance. Normal cultures require no other 

 food than minerals, carbohydrate, and a single vitamin, biotin (Butler, Robbins, 

 and Dodge, 1941). Either spontaneously or under violent treatment (with x-rays, 

 ultra-violet radiations, or mustard gas) the cultures give rise to many mutations, 

 behaving as Mendelian recessives, each consisting of the inability to synthesize 

 some one vitamin or amino acid. These observations mean that life in its aspect of 

 metabolism consists of unit chemical processes, each controlled by a specific enzyme, 

 each enzyme being dependent upon a specific area in a specific chromosome. 



Among stromatic Sphaeriales, Glomerella, with conidial stages identified as 

 Gloeosporium or Colletotrichum, attacks many plants; G. cingulata causes the bitter 

 rot of apples. Valsa, Diatrype, and Diaporthe are numerous in species. Endothia 

 parasitica causes the chestnut blight, destructive in the eastern United States. 

 Xylaria, Daldinia, and other genera are saprophytic on wood; the former produces 

 black fruits, club-shaped or branched; the latter, fruits of the form of black knobs 

 which may reach the size of golf balls. 



Among Hypocreales, Nectria cinnabarina is common as a saprophyte on dead 

 twigs of poplar. It produces small wart-like red stromata which bear first conidia, 

 then perithecia. Claviceps purpurea causes a disease of rye; it produces conidia of 

 various types, and converts the grains of rye into sclerotia. These bodies are called 

 ergot; they are extremely poisonous, sometimes dangerously so, because they may 

 be ground with the grain. They are used in medicine. After lying in the earth through 

 the winter, the sclerotia send up fruits of the form of a stalk bearing a knob consisting 

 of radiating perithecia. Cordyceps kills subterranean larvae or pupae of insects and 

 then sends up a stalk bearing an elongate head of many perithecia. 



