INTRODUCTION TO CRYPTOGAMIC BOTANY. 271 



either naked, or contained in a distinct variously shaped cavity, 

 the walls of which often consist of closely compacted cells, 

 whose coats are frequently carbonized, and the apparatus is 

 then called a perithecium. These two conditions are com- 

 bined with various modifications of the mycelium, and the 

 stroma to which it gives rise ; and hence the external form and 

 appearance are often so different as, at first sight, to suggest 

 anything but close affinity, even where undoubted affinity 

 exists. The higher forms are modified again by the circum- 

 stance that many species are altogether subterranean in 

 their habits ; and as in truly subterranean forms it is all but 

 impossible that the delicate sacs of the hymenium should be 

 developed in immediate contact with the earth, that important 

 stratum, which in allied genera was external, becomes internal 

 by introversion or complication of the walls. It is amongst 

 these hypogeous species that the most beautiful and compli- 

 cated fruit is produced, affording the most exquisite objects 

 for the microscope. 



275. Though the species are numerous, and, doubtless, many 

 of them are wholesome, their size is in general so small as 

 to make them iiisignificant as articles of food, though there 

 are some eminent exceptions. Others, again, are so hard and 

 tough as to make their consumption almost impossible, though 

 one species, at least, amongst the carbonaceous Fungi, is eaten. 

 Morells and Truffles are well-known objects of luxury, and, 

 whether fresh or dry, always command a high price ; and there 

 are some, as Helvella esculenta (Fig. 13, a), closely allied to 

 the Morell, which are equally good as articles of food. Morells, 

 indeed, are in such demand on the continent, that in some 

 parts of Germany the peasantry were in the habit of burn- 

 ing down large tracts of woodland, having found that the 

 burnt soil is peculiarly productive. This practice existed 

 at one time to such an extent, that it was found necessary 

 to enact laws for its suppression. Cyttaria forms an import- 

 ant item in the food of the Fuegians ; and Hypoxylon 

 vernicosuvi, the stroma of which may be compared with 

 that of D'Urvillma utilis, is consumed by the Bhoteansin 

 the Himalayas. 



