MACROGONIDIA. 



[ 410 ] 



MAGNESIA. 



MACROGONIDIA.— A name applied by 

 the Germans to the larger form of ciliated 

 zoospore, found in many Confervoid Algae, 

 associated with a form much smaller, distin- 

 guishedasMicROGONiDiA. SeeZoospoRES 

 and Hydrodictyon (p. 332). 



MACROSPORIUM, Fr.— A genus of 

 Dematiei (Hyphomycetous Fungi), growing 

 upon decaying vegetable matters, correspond- 



Fig. 444. 



Fig. 445. 



Macrosporium bulbotrichum. 

 Magnified 200 diams. 



ing to Septosporium, Corda, and Helmispo- 

 rium, Duby. Several species are British. 

 M. Cheiranthi, Fr., common on wallflowers 

 and stocks ; M. Brassicce, Berk., on cabbage- 

 leaves ; M. sarcinula on gourds ; and M. 

 concinnum, on rotting decorticated willow 

 twigs. We have found one species among 

 the OiDiUM of the vine-fungus. 



BiBL. Berk. Brit. Flor. ii. pt. 2. p. 339, 

 Ann. Nat. Hist. i. p. 261. pi. 8. fig. 10, vi. 

 p. 435. pi. 12. fig. 21 ; Fries, Summa Veget. 

 p. 501, Syst. Mycol. iiii. p. 274 ; Corda, 

 Icones Fung. i. p. 175. 176. 188. 



MACROTHRIX, Baird.— A genus of En- 

 tomostraca, of the order Cladocera and 

 family Daphniadae. 



Char. Five pairs of legs ; beak directed 

 forwards ; superior antennae of considerable 

 size, one jointed, and pendulous from the 

 beak ; inferior antennae two-branched, pos- 

 terior branch four-, anterior three-jointed, 

 and with a very long filament arising from 

 the end of the first joint ; a black spot at the 

 root of the superior antennae. 



M. laticornis (PI. 14. fig. 25). Shell 

 oval, smooth, anterior margin strongly 

 ciliated ; eye areolar. 



Found in ponds. 



M. roseus. Eye without an areola; su- 

 perior antennae longer and more slender 

 than in the above. 



Probably a variety of the last. Found in 

 Scotland. 



BiBL. Baird, Brit. Entomostr. p. 103. 



MADOTHECA, Dumortier {Jungerman- 

 nia, L.). — A genus of 

 Jungermannieae (Hepa- 

 ticaceae), containing two 

 British species, one, M. 

 platypliylla (fig. 445), 

 common on walls, rocks 

 and trees ; the other, M. 

 Icevigata, found on alpine 

 rocks. The sporange is 

 borne on a short stalk, 

 globose, and bursts by 

 four convex valves, from 

 which the elaters are 

 quite free. The globose 

 persistent epigone is seen 

 in the figure inside the 

 two-lipped perigone. 



BiBL. Endl, Gen. Madotheca platyphylla. 



Plant. Suppl. i. p. 1341 ; ^^^^n. s diams. 

 Hooker, Brit. Flora, ii. p. 125, Brit. Jun- 

 germann. pi. 35. 40, and Supp. pi. 3; Ekart, 

 Synops. Jungermann. p. 52. pi. 3. fig. 24. 

 pi. 6. fig. 44. 



MAGNESIA, Salts of. 



Ammonio-phosphate of magnesia or triple 

 ])hosphate. This salt is frequently met with 

 in animal secretions which have undergone 

 decomposition, also in calculi. The most 

 common forms are prismatic, and figured in 

 the group a, PI. 9. fig. 1, but their varieties 

 are endless. Those of the above group are 

 frequent in decomposing urine, blood, faeces, 

 &c. Those in group c are occasional in 

 urine. Those of group d are found in the 

 contents of the vesiculae seminales. The 

 forms e and / are rare. Fig. 2 a, b repre- 

 sents the so-called penniform crystals, or 

 rather groups of crystals (prisms) occasion- 

 ally found in urine. Fig. 3 represents the 

 stellate form, occasionally found in urine ; 

 sometimes the minute and imperfectly 

 formed crystals of fig. 4 are met with in the 

 same liquid. 



The crystals belong to the rhombic system. 

 The prismatic crystals were formerly con- 

 sidered as consisting of a neutral, and the 

 feathery of a bibasic salt ; but the composi- 

 tion of the two is the same, and the variation 

 in form depends upon the conditions under 

 which they are produced. 



The prismatic forms may be prepared 

 artificially by allowing urine to decompose ; 

 or by diluting this secretion with water, and 

 gradually stirring in very dilute solution of 



