702 REPOET— 1888. 



4. A Lily Disease. By Professor H. Marshall Ward, F.B.S. 



5. On the Morphology of the Pitcher of Ne2}enthes, 

 By Professor BowEK, F.L.S. 



6. On Adelpliotaxy : an imdescrihecl Form of Irritahility. 

 By Professor Marcus M. Haktog, B.Sc, M.A. 



In Achlya, a genus of Saprolegniese, the zoospores lie in tlie sporange before 

 liberation closely appressed together, with their long axes parallel, instead of 

 showing the rotatory hustling movements of other species. In liberation, instead 

 of separating and swimming off, each on its own account, they remain near the 

 mouth of the sporange, each in turn edging its way in between those that have 

 already escaped with its narrower flagellate (anterior end inwards). They thus 

 form a hollow sphere, each zoospore rotating round its long axis (radial to the 

 sphere) before encysting in its place. The only explanation that will fit these 

 phenomena is that these zoospores are endowed with a peculiar irritability in vii'tue 

 of which they tend to place themselves close together side by side, with their 

 long axes parallel. This irritability is only exerted at a short distance ; for, if a 

 zoospore be pushed as little as its long diameter away, whether by accident or 

 design, it fails to find its place, but swims off to and fro, instead of rotating in situ, 

 before encysting. 



In a critical review, now in the press, of a paper by Eothert, I have given the name 

 ' adelpliotaxy ' to this form of irritability, consisting in the tendency of sponta- 

 neously motile cells to assume definite 2)osit ions toith regard to their felloivs. 



Leaving aside the kindred question of tissue-formation and the processes in the 

 embryo-sac of Phanerogams, adelphotaxy is of rare occurrence in the Vegetable 

 Kingdom. Two good instances occur in the Chlorophytes. In Pediastrum the 

 contents of each cell of the flat disc break up into 16 (or 32) zoospores, which 

 swarm in the cell, and then unite edge to edge to form a new disc. So in each 

 cell of a Hijdrodictyon the many thousand zoospores unite end to end to form a new 

 network with hexagonal meshes. 



In many of the Myxomycetes the plasmodia aggregate together before fructifi- 

 cation to form the compound masses termed asthalia ; possibly even the very forma- 

 tion of Plasmodia may be regarded as a mode of adelphotaxy. 



We may perhaps go a step further and ascribe the parallel or converging courses 

 of Fungus hyphce to form mycelium strings, fruit bodies, and pseudo-parenchyma 

 as extreme cases of adelphotaxy. 



I think this principle affords a ready explanation of many cases of cellular 

 aggregation in the animal embryo, and the formation of the spermatophores of many 

 animals, notably Limicolous Worms. 



The relations of sexual and isogamous union of gametes to adelphotaxy are 

 obvious ; for, though in some cases of sexual union cbemotaxy has been shown 

 by Pfeffer to be involved in bringing the active gamete from a distance, that will 

 not cover the actual fusion of the two cells. 



Zoological Depaetmekt. 



Report of the Committee for reporting on the 2'>'>'esent state of our Icnoio- 

 ledge of the Zoology and Botany of the West India Islands, and taking 

 steps to investigate ascertained deficiencies in the Fauna and Flora. — 

 See Reports, p. 437. 



