44 PROCEEDINGS OP THE AMERICAN ACADEMY 



rolled back, gradually disappears over the whole disk. The excii)le of 

 the mature apothecium then is not elevated above the hymenium, and 

 the apothecium itself resembles in cross-section a shallow cup, the sides 

 of which are elevated above the thalliue surface, but not above the hy- 

 menium. Carpologically therefore, as well as structurally, Hydrothyria 

 presents a marked atHuity to Pannaria. It not infrequently happens 

 that a double apothecium is formed. Both surfaces of the thallus be- 

 ing often, from their upright position in the water, equally exjDosed to 

 external influences, the tendencies are only slightly, if at all, in favor 

 of apothecial development on one surface rather than on the other, so 

 that the primordium may give rise to a hymenium on both surfaces, 

 and we have as the result two apothecia on opposite surfaces of the 

 thallus. (Plate V. Fig. 32.) This equalization of tendencies pervades 

 the whole thallus, there being nothing in sections to distinguish accu- 

 rately one surface from the other, except the venation and the occa- 

 sional feeble and scanty growth of short, hair-like processes where one 

 surface by chance comes in contact with the substratum. 



By employing the same treatment as heretofore, the asci and para- 

 physes may be traced to their origin with comparative ease, owing to 

 the non-gelatinous quality of the hymenium. (Plate IV. Figs. 26, 27.) 

 Treatment with iodine stains the asci alone blue, and the presence of 

 larger cells in the hypothecium is no longer visible. This disappear- 

 ance of cells previously seen to exist may be explained in one of two 

 ways. The primordium, and therefore the hypothecium, as has been 

 shown, are formed by a copious branching of the medullary hyphae, 

 these branches being much finer than the hyphje from which they arise. 

 Now it is almost to be expected that before the dense tissue is fully 

 formed, and while the branches are still arising, it might easily happen 

 that portions of the medullary hyphfe would become enclosed in this 

 forming tissue. They would remain visible until completely over- 

 grown, when they would become compressed and distorted to such a 

 degree as to be no longer recognizable. If however we choose to 

 consider them as analogous to the Woronin's hypha of certain Asco- 

 mycetea3, notwithstanding their lack of any regular arrangement, we 

 must believe that we have to do here with a form of reproduction 

 analogous to that seen in Xylaria, and said to be characterized by the 

 disorganization and disappearance of the Woronin's hypha and the 

 absence of a trichogyne. Following out this analogy, we are led to 

 the conclusion reached by De Bary in the case of Xylaria, that " the 

 ascogenous cells and hyphge do not spring from a distinct ascogonium, 

 but, like the paraphyses, from parts of the primordium, while the 



