NOTES AND MEMORANDA. 313 



hyphema, the original fundamental tissue out of which the gono- 

 hyphas are themselves differentiated. This can be best detected in 

 the hypothalline tissue, at the point of origin of the rhizines. Its 

 cells are very minute, and have not the elongated form of those of 

 the gono-hyphse, but contain, like them, microgonidia. It will be 

 observed that the structure and development of Nostoc agree, in every 

 essential respect, with that just described of ordinary lichens. 



In addition to the ordinary mode of reproduction of the thallus of 

 lichens which the author terms hlastesis, there is another which is less 

 known, and to which he specially calls attention. The bodies which 

 he calls hormospores, now described for the first time, are similar in 

 their mode of origin to the stylospores or teleutospores of fungi. They 

 are colourless, and contain a number of moderately large microgo- 

 nidia, and are produced on the rhizines and other parts of the lichen, 

 as the terminal cells of special hyphae. When about to propagate, 

 the hormospore divides into a number of cells, the microgonidia at 

 the same time also increasing rapidly. The mother-cell then de- 

 liquesces into a jelly, the microgonidia at the same time developing 

 into metrogonidia. 



The peculiarity of lichens, which distinguishes them from every 

 other class of vegetable productions, is that all the three kinds of 

 tissue above described are capable of independent reproduction ; but 

 that no one of the three can itself reproduce a lichen. A combination 

 of all three is necessary for this purpose ; and this is the cause of the 

 remarkable appearance which has given rise to the theory that a 

 lichen is a compound structure of one organism parasitic upon 

 another. 



In a subsequent paper * the well-known lichenologist. Dr. J. 

 Miiller, of Geneva, confirms Dr. Minks's statement as to the develop- 

 ment of the gonidia of lichens out of microgonidia. He states that 

 he has been able to make out the microgonidia with ease, with a 

 Swift's ^-inch objective (a power of 360), after subjecting the lichen 

 to the chemical treatment recommended by Dr. Minks; and with 

 Hartnack's immersions No. 10 and No. 15 without any chemical 

 preparation, in both fresh and dried lichens. Dr. Miiller detected 

 microgonidia in all the cells, both vegetative and reproductive, of the 

 entire lichen ; in the rhizines, cortical cells, medullary hyphfe, para- 

 physes, young asci, spores, basidia, and spermatia, but most distinctly 

 in the medullary hyphfe, where they form a light greenish bead-like 

 chain or row of minute balls in the axis of the hyphae, with a diameter 

 of about o^oVo' t^ s'ffVff ^™' They are still more easily seen in the 

 hyphae of heteromerous lichens, as Physcia and Parmelia ; and they 

 can also be made out without difficulty in vertical sections through 

 the thallus of crustaceous and foliaceous lichens. Intermediate con- 

 ditions in all stages may be observed between microgonidia and goni- 

 dia, which gradually become free by absorption of the hyphae, and 

 then divide. Dr. Miiller concludes, therefore, that the gonidia" of 

 lichens are not foreign bodies imbedded in their tissue, but that they 

 originate in the hyphae, as the spores in the asci. 



* 'Flora,' xxxvi. (1878) 479. 



