SECT. I 



CRYPTOGAMS 



399 



thickened epi.spore. They are set free in the soil by tlie breaking down of the 

 asci and of the wall of the fructification. 



The fructifications of many of the Tuberaceae are edible C*^), and have an aromatic 

 odour and taste. They are, for the most part, obtained from France and Italy. 

 Of the edible varieties, the most important are the so-called black truffles 

 belonging to the genus Tuber, viz. Tuber hrumale, melanosporum (Perigord Truffle), 

 aestivum, mcscntcrieum. The fructifications of these species have a warty cortex of 

 a black, reddish-brown, or dark brown colour. The white truffle, Choiromyces 

 meandriformis, the external surface of which is pale brown, is also edible. 



The fructifications when very young are open as in the Discomycetes. The 

 Truffles seem most nearly related to tlie Helvellaceae. 



Order 6. Exoasci C^'*) 



The most important genus of this group of Ascomycetes is Taphrina (including 

 Exoascus), the species of which are parasitic on various trees. They develop in 

 part annually beneath the cuticle of the leaves, 

 causing discolorations of these organs ; their 

 mycelium persists during the winter in the 

 tissue of the host, so that a constant recurrence 

 of the disease takes place. The presence of 

 the mycelium in the tissues of the infected 

 part causes the abnormally profuse develop- 

 ment of branches known as "Witches'- krooms. 

 Taphrina Carinni i)roduces the abnormal growths 

 occurring on the Hornbeam ; Taphrina Cerasi 

 those on Cheny trees. Tapltrina deformans 

 attacks the leaves of the Peach and causes them 

 to curl. Taphrina Pruni is parasitic in the 

 young ovaries of many species of Primus, and 

 produces tlie malformation of the fruit known 

 as "Bladder Plums," containing a cavity, the 

 so-called "pocket," in the place of the stone; 

 the mycelium persists through the winter in 

 the branches. In the formation of asci, the 

 copiously-branched mycelium ramifies between 

 the epidermis and cuticle of the infected part. 

 The individual cells of the mycelium become 

 greatly swollen and grow into club-shaped tubes, 

 which burst through the cuticle and, after cut- 

 ting off a basal stalk-cell, are usually converted 

 into asci with eight spores (Fig. 330). As in other Ascomycetes the young ascus 

 has two nuclei which fuse, and the resulting nucleus undergoes three divisions to give 

 the nuclei of the ciglit spores. The numerous asci are closely crowded together. 



The spores, which bud in water or sugar solution, frequently germinate while 

 still enclosed within the asci (Fig. 330, ftg, a^), and give rise by budding to yeast- 

 like conidia, e.g. in Taphrina Pruni. 



The Exoasci are perhaps to be regarded as reduced Ascomycetes, in which the 

 sexual organs have become comple ely suppressed. 



Fig. 330. — Taphrina Pruni. Transverse 

 sectidii through tlie epidprinis of an 

 infected plum. Four ripe asci, «i, Oo 

 with eight spores, n.j 04 with yeast- 

 like conidia abstricted from the 

 spores ; st, stalk-cells of the asci ; m, 

 tilanients of the mycelium cut 

 transversely ; cut, cuticle ; ep, epi- 

 di'rmis. (After Sadebeck, x liOO.) 



