1139 



WA)t Ercasun? at JSntanjn 



[thap 



however, consists in tlie fact that the 

 spore of sacrogens when germinating 

 produce either a cellular mass or plant, in 

 which bodies called archegoniaare formed, 

 which by impregnation produce from an 

 embryonic cell either a new plant or a 

 spore-bearing capsule, while in thallogens 

 no. bodies corresponding to archegonia 

 are ever produced. The spores of Pac- 

 cinimi and .Ecidiacei indeed produce a sort 

 of preparatory organism described above 

 under the name of Protospore, but it has 

 nothing homologous with the prothallus 

 of acnigens, arising as it does from the 

 mycelium of the fungus, and not from the 

 immediate germination of the spores. 

 The only apparent exception amongst 

 acrogens is that of Characece, but the in- 

 fant state of the nuclei has not at present 

 been accurately observed. 



Thallogens then include the two vast 

 tribes of algals and fun sals, of which the 

 latter are divisible into two main divisions 

 Fcxgi and Lichexs, to which heads, to- 

 gether with that of Alg^e, we must refer 

 for particulars. [M. J. B.] 



THALLOPHYTES. Thallogens. 



THALLU3. A fusion of root stem and 

 leaves into one general mass. This te"rm, 

 also used to express the part of thallogens 

 immediately bearing the fructification, is 

 applied more particularly to the cellular 

 mass in which the perithecia are inclosed 

 in tiypoxylon, which is however more f re 

 quently called stroma, or still more espe- 

 cially to the whole vegetative system of 

 lichens. This consists of several distinct 

 strata, which it is of much consequence to 

 distinguish in the description of lichens. 

 The external or cortical layers consist of 

 closels-packed often cartilaginous cells, 

 formed by the anastomosing of the tips of 

 the central branched threads , next to this, 

 in the more typical lichens, is a layer con- 

 sisting of globose green bodies called 

 gonidia, generated from the free tips of 

 some of the same threads which produce 

 the cortical stratum. In collemals these 

 globules form little necklaces, are quad- 

 ripartite as in Omphalaria, or fissiparous— 

 produced that is by repeated vertical divi- 

 sion, as in Synalyssa and Paulia, This 

 stratum is called the gonimic. 2sext to 

 this comes the filamentous medullary stra- 

 tum, which gives-rise to all the others, and 

 from which alone the fruit is produced. 

 This consists of a mass of threads spread- 

 ing in every direct ion, and constituting the 

 essential part of the lichen. After tins 

 follows occasionally a second gonimic. 

 stratum, and then one similar to the cor- 

 tical, giving out fibrous processes or floeci. 

 These however may be absent, the medul- 

 lary stratum resting without any especial 

 condensation upon the matrix. The medul- 

 lary stratum may be clearly traced, giving 

 rise to the two first, and also to the con- 

 densed tissue which immediately bears the 

 asci or threads of the spermatia. Though 

 the walls of the apothecia or spermogonia 

 may be confluent aoove with the cuticle, 

 from which they differ very little in struc- 



ture and often in substance, they may he 

 j distinctly traced below to the medullary 

 threads. In Coccocarpia, if indeed it be 

 | not a mere parasite as Tulasne suggests, 

 ' there is no excipulum ; but the fructifying 

 mass is at first inclosed in the medullary 

 stratum, through which it at length bursts. 

 Our own observations accord, as far as the 

 materials which we have had at our dis- 

 posal go, with Tulasne's, and we believe all 

 the genera of the natural order of Cocco- 

 carpei to he parasitical, and the entire 

 order anomalous. The whole plant, in fact, 

 appears to consist of fruit without any 

 especial thallus, though spermogonia exist 

 as well as in other lichens. In Cceiwgo- 

 riium, which is apparently allied to Biatora, 

 the medullary stratum is free, and ex- 

 panded like the mycelium of a fungus, 

 with an almost total suppression of the 

 upper stratum. Whether this is the effect 

 of peculiar conditions or a normal struc- 

 ture, as is most probable, remains to be 

 I seen. A Biatora has however been found 

 | in Switzerland, which suggests doubts. In 

 I some abnormal forms, as Leprana, the 

 i gonimic stratum is predominant, while in 

 ! L: Iqtebrarum the threads of the medullary 



stratum are still evident. [M. J BJ 



' THAMNIFM. The branched bush-like 



thallus of lichens. 

 I THA5IKOMTCES. A genus of Fungi 

 i allied to Sph&ria and Hypoxylon, in which 

 the common thallus or stroma is branched 

 or much elongated, and the perithecia are 

 formed of the medullary substance coated 

 with the bark. Most of the species, which 

 are very curious, are tropical ; but one, 

 T. hippotrichioid.es, is not uncommon in 

 , England in cellars or damp rooms, on old 

 ! matting made of Scirpus lacustris, or on 

 hemp sacks. The plant is about the thick- 

 ; ness of a horsehair, much branched, and 

 bearing ovate fruit scattered over the stem 

 or branches. As far as this species is con- 

 cerned, the genus seems the same with 

 lihizomorpha as defined by Fries. The 

 asci are at length absorbed, and the dark 

 elliptic sporidia seem naked. [M. J. B.] 



! THAMXOPTERIS. A genus of asple- 

 nioid ferns, with thick erect caudiees, and 

 simple coriaceous fronds, remarkable in 

 the asplenioid group for the submarginal 

 vein, which unites the apices of the pa- 

 i rallel forked oblique veins, and by the 

 long narrow linear crowded indusiate sort! 

 ' The typical species is often called the 

 i Bird's-nest Fern, and has been severally 

 i called Asplevnun Nidus and Neottopteris 

 I vulgaris ; it is represented, growing on a 

 I Ficus, in Plate jo, fig. /. The species are 

 I few in number, and chiefly Eastern, their 

 | head-quarters being India, the Indian 

 Archipelago, the Pacific Islands, Australia, 

 &c. One of the finest is T. Musw/olia, a 

 native of the Philippine Islands. [T. M.] 



THAPSIA. The plants belonging to 

 this genus of Umbelliferte were in very 

 ancient times celebrated for their medici- 

 nal products— the Cyrenean Silphium or 

 Laser Cyreniacum being generally sup- 



