HARDWICKE'S SCIENCE-GOSSIP. 



49 



GRAPHIC MICROSCOPY. 



By E. T. D. 



NO. XV. — FOLYSIPHONIA ELONGATA. 



HEN plants 

 were studied 

 only in connec- 

 tion with their 

 medicinal uses, 

 the marine 

 algae escaped 

 scrutiny, and 

 were compara- 

 tively neglected 

 and unclassified, 

 the earlier sys- 

 tematic botan- 

 ists scarcely 

 recognised 

 their existence, 

 and it is only in 

 recent times 

 that algology 

 has assumed the 

 importance of 

 a scientific speciality. This is undoubtedly due 

 to the improvement in the microscope and its 

 accessories. Without this instrument the beauty 

 of many of the minute species, and certainly their 

 structure and mode of fructification, could never have 

 been completely approached, or understood. 



In comparison with land plants, the sea-weeds 

 differ greatly, and offer many characteristic peculiari- 

 ties, depending on the medium in which they grow, 

 influenced by abrupt changes of heat and light, 

 affected by localization. 



When botany became a science, sea-weed history 

 arrested the attention of patient observers, and the 

 dim horizon was illuminated by the researches 

 (among others) of Greville, Carmichael, Agardh, 

 whose labours were eventually consolidated, and 

 enriched by Professor Harvey in the " Phycologia 

 Britannica," 4 vols. 1846-51, the greatest work on 

 the subject. It might be presumed that to supplement 

 such results would be impossible, that nothing 

 No. 243. — March 1885. 



remained ! But new varieties are yet to be dis- 

 covered, and important facts traced and investigated. 



Of the Florideous Alga; (red filamentous sea- 

 weeds), the families Delesseriacese, Ceramiaceae, and 

 Rhodomelaceae, are the most delicate, and, under 

 microscopic examination, singularly beautiful. Poly- 

 siphonia elongata, the subject of the plate, is a genus 

 of the latter family, and exhibits a filiform articulated 

 frond, the filaments interrupted at the joints by 

 tubes sufficiently transparent to reveal the purple or 

 pink contents. In this family the number of the tubes 

 are distinctive of the genus. The circles of longi- 

 tudinal cells surround a central axis, not unlike the 

 wood bundles enveloping the pith of a Dicotyledonous 

 stem, and very elegant microscopic objects are 

 transverse sections of such fronds, showing the 

 appearance of rosettes — these twisted filaments are 

 covered with a thin cellular tissue ; the disposition 

 and arrangement of the cells of minute algae, with 

 the brilliant colour of the endochrome, in multi- 

 farious combinations, are amongst the most attractive 

 objects of microscopical investigation. 



The specimen figured exhibits a condition of 

 fructification resulting in " ceramidia," cup-like or 

 pitcher-shaped capsules, with membranaceous walls, 

 thin and filmy, attached to the sides of the branches, 

 and containing at the base numerous pear-shaped 

 spores. The drawing was made from a permanently 

 mounted preparation, necessarily somewhat flattened ; 

 but in a fresh condition, in a deep receptacle, the 

 ceramidia show a more decided urn-like, or ovate 

 condition; under other conditions, " tetraspores " 

 are developed in the central cells of the fronds, and 

 "conidia," and " antheridia," in elongated whitish 

 sacs at the summit of the branches. 



Specimens are frequently found on scallop shells, 

 and at very low tides (after heavy weather) some 

 rare forms may be collected, which, under ordinary 

 circumstances, could only be procured by dredging. 

 On a shelving coast terraced with rocks, it may be 

 observed that the algae near high-water mark are 



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