ORDEE LECANORALES (thE DISK LICHENS) 215 



they germinate, one cell becoming the foot and the other developing the 

 remainder of the plant. The full nuclear phenomena of fertilization have 

 not been worked out because of the difficulty of finding the fungi in the 

 proper stages of development and the extremely difficult technique of 

 sectioning and staining. 



Only a very few genera and but few species of this order were known 

 until the monumental work of Dr. Roland Thaxter, published in succes- 

 sive parts in 1895, 1908, 1924, 1926, and 1931, revealed the fact that this 

 order contains hundreds of species, dozens of genera, and several families. 

 Since the appearance of the first volume of this marvelous work other 

 mycologists also have added numerous species to those described by Dr. 

 Thaxter. Not only are these fungi found on beetles (Coleoptera) but also 

 on Hymenoptera, Diptera, and various other orders of insects. In view 

 of the fact that of the 600,000 to 1,000,000 described species (and possibly 

 as many or more as yet undescribed species) of insects only a few thousand 

 have been examined for the presence of these parasites it seems reasonable 

 to suppose that the number of species, genera, and even families of this 

 order may be greatly increased in the future. 



The relationship of Laboulbeniales to the other orders of Ascomy- 

 ceteae is not very close. The spore fruit is unlike that of any other mem- 

 bers of this class and the vegetative structure finds few analogies. In the 

 sexual reproduction the formation of functional, separable sperm cells 

 is known in Collema and other lichens and in Pezizales, Sphaeriales, and 

 other groups. In most of these however the sperms are not produced 

 endogenously as naked cells as is true of most of the Laboulbeniales but 

 seem to have thin walls even in those cases where endogenous formation 

 does occur. The "archicarp" of the Laboulbeniales reminds one remark- 

 ably of the condition in some of the Florideae where the archicarp is 

 surrounded by protective cell layers with merely the trichogyne exposed. 



The following orders: Lecanorales, Pezizales, Tuberales, Hysteriales, 

 and Taphrinales all produce spore fruits that may be considered as typical 

 or modified apothecia. They are often or in part included under the group 

 name Discomycetes. 



Order Lecanorales (The Disk Lichens). These constitute a large group 

 of organisms which have in common the production of apothecia and 

 which show a specialized form of parasitism on land species of Chloro- 

 phyceae and Myxophyceae. The validity of the maintenance of this group 

 apart from the Pezizales is, to say the least, very doubtful, but until the 

 reproductive processes, especially the behavior of the sexual nuclei, are 

 better known in both groups it is perhaps better to follow custom and 

 consider the two orders separately. Possibly when such studies have been 

 carried out in all the more important genera that produce apothecia the 

 system of classification of both orders will have to be entirely revised. 



