ACHLYA. 



ACHNANTHES. 



seated on the end of the sporange. During 

 the formation of these sporanges and the go- 

 nidia, after the septum has been completed, 

 the tube sends out lateral branches from just 

 below it, which sometimes equal the spo- 

 range in length by the time the latter dis- 

 charges its contents ; then this branch be- 

 comes developed as a sporange, either at its 

 summit or in its whole length, or, when the 

 branch is very short, the portion of the main 

 tube below the first septum becomes a spo- 

 range. Sporanges of a third rank may suc- 

 ceed to those of the second rank, and so on, 

 until the plant has exhausted the supply of 

 food at its service. 



Achlya prolifera also produces, though 

 more rarely, globular or spindle-shaped spo- 

 ranges, borne on special, short, lateral branch- 

 es, in which are developed resting spores, 

 characterized by a larger size, double cell- 

 membrane, and by the absence of the cilia 

 and consequent motion. The mode of their 

 development is similar to that of the active 

 gonidia, but they are much fewer in number, 

 sometimes as many as twenty, sometimes 

 only four, three, two, or even one being pre- 

 sent in a sporange. When a number occur 

 in a spindle-shaped sporange, they are ranged 

 in two rows, alternately, so that each is par- 

 tially interposed between its two opposite 

 neighbours. Their diameter varies from 

 1 - 1250 to 1 -750 of an inch, the colour brown- 

 ish, displaying numerous oil-drops in the 

 granular contents when mature. The spo- 

 ranges producing them display a number of 

 round orifices when the spores are ripe, but 

 the spores appear to escape by the decay of 

 the walls. These resting spores may remain 

 unchanged in water for a long time when no 

 suitable nidus exists, and then will quickly 

 germinate if a dead insect or similar object 

 is thrown in. 



2. Achlya prolifera of Pringsheim, Unger, 

 Carus and others (Saprolegnia ferax, Kiitz- 

 ing), differs from the true A. prolifera in two 

 important points : 1. The sporanges do not 

 produce the capitules, by the accumulation of 

 the daughter-cells giving birth to the active 

 gonidia at their summits, but the active go- 

 nidia are produced directly from the contents 

 of the sporange, and begin to move even 

 before they escape from this. 2. The later 

 sporanges are not formed by lateral branches, 

 but the septum forming the bottom of the 

 first sporange grows up into the empty 

 cavity of this and swells into a new spo- 

 range within the old one, which remains as a 

 second, outer coat. In other respects there 



is no difference in the general mode of deve- 

 lopment. S. ferax is ordinarily of smaller 

 diameter ; it produces globular cases of rest- 

 ing-spores in a similar manner; and these 

 occur mostly after the gonidial sporanges, 

 generally at the ends, but occasionally in the 

 middle of the tubes. The resting-spores are 

 from 1 to 40 here, while the active gonidia 

 are from 5 to 150, the number depending in 

 each case on the size of the sporange, not 

 upon the size of the spores or gonidia, which 

 is tolerably regular. Pringsheim states that 

 starch occurs in the contents of the resting- 

 spores of S. ferax. 



BIBL. A description of the supposed spe- 

 cies will be found in Kiitzing's Species Alga- 

 rum, p. 159. For further information on the 

 development, see Al. Braun's Rejuvenescence 

 in Nature, translated for Ray Society, 1853, 

 pp. 188,268; Pringsheim, Nova Acta, xxiii. 

 pt. 1. p. 397-460, 1851; Anton, de Bary, Bo- 

 tanische Zeituno, x. p. 473, 1 852. Also Un- 

 ger, in the Linncea for 1843, p. 129 (trans- 

 lated in Ann. des Sc. nat. 3 me ser. tome ii. p. 5. 

 pi. 1. 1844); M.eyen,Pflanzenphysiologie,m. 

 457 ; Nageli, Zeitschrift fur fViss. Botanik, 

 heft 1. p. 102, heft 3,4. p. 28 (Ray Society's 

 Reports, 1845, p. 278, 1849 ; p. 101); Thu- 

 ret, Ann. des Sc. nat. 3 me ser. t. xiv. p. 20. 

 p. xxii. 1851; Ch. Robin, Hist oire des Vege- 

 taux Parasites, 2nd edit. 1853, p. 372. A list 

 of all the writers who had treated of Achlya 

 before 1843, is subjoined to Unger's Essay 

 in the Linncea. 



ACHNANTHES, Bory. A genus of Dia- 

 tomaceae. 



Char. Frustules either single, in pairs, or 

 united into a straight filament, frustules 

 curved in front view, without septa; a punc- 

 tum (orifice) at the middle of the lower mar- 

 gin of the undermost valves. 



The individual frustule, when single, or 

 the lowermost when they are united, is in 

 some species furnished with a stipes or stalk, 

 arising from one end of the lower margin, 

 in others this is absent ; and the latter have 

 been separated from the former to make a 

 distinct genus, Achnanthidium, principally by 

 this character. Side view of frustules ellip- 

 tical, oblong or linear, sometimes slightly 

 constricted in the middle ; markings of upper 

 and lower valves different, the upper (PI. 12. 

 fig. 2) exhibiting transverse rows of dots 

 (appearing like striae under a low power) in- 

 terrupted by a longitudinal line, the lower 

 (PL 12. fig. 3) being also furnished with 

 transverse rows of dots, interrupted by a stau- 

 ros, as also by a longitudinal line which in 



