NOTES AND MEMOKANDA. 79 



ceiihalodia of PeUigera aphthosa, which I have followed from the first 

 commencement of the invasion of the alga by the hypha ujj to the 

 complete development of the cephalodia." 



After a reference to the descrijjtion given by Acharius of the 

 cejihalodia in question, the author thus details his own investiga- 

 tions. 



In vertical sections of a cephalodium of PeUigera aphihosa com- 

 pletely developed, the central part consisted of a tissue of filaments 

 loosely interlaced with hyjjha, between which wore masses of bluish 

 gonidia, arranged without any apparent order, whilst the j^eriphery 

 was formed of a homogeneous brown cortical layer, much thicker on 

 the superior side than on the inferior, and consisting of pseudo- 

 parenchymatous tissue. From the inferior surface descend a row of 

 radical hairs (rhizines) of a dark brown, of which the membranes, very 

 much thickened, penetrate to the soil through the openings of the 

 thallus of Peltujera and interlace themselves with the similar hairs of 

 the latter. The body itself of the cephaludium is in contact with the 

 edges of the opening of the thallus, like a cover, and without any 

 organic relationship with it. If the general form of the cephalodium 

 were examined, w-ithout knowing the history of its development, we 

 should suppose that it must be a homeomerous lichen growing para- 

 sitically on the PeUigera and bearing a resemblance to Pannaria 

 triptophijUa, for example. The gonidia of the cephalodia are blue, and 

 consequently belong to the phycochromaceous algas ; whilst those of 

 the lichen itself are of a light green and belong to the chlorophy- 

 laceous. They are also distinguished from one another by their size ; 

 the former attain -010 mm., the latter only •006 mm. Both are 

 oblong, often triangular or square, but rarely round. In examining 

 the form of the gonidia of the cephalodia it is impossible to decide to 

 what algfe they belong. 



To solve this question, the author took advantage of the method 

 of culture employed by MM. Famintzin and Baranetsky, in their 

 researches on the gonidia of C lUema pulposum and PeUigera canina, 

 and sowed in soil previously boiled some sections of cephalodia 

 (examined under the microscope to assure the absence of any foreign 

 organism), and then placed under a bell-glass in a damp atmosphere. 

 At the end of two weeks and a half, when the hyphae were entirely 

 destroyed, there could be remarked on the surface of the sections a 

 great number of small gelatinous balls, each containing three or four 

 bluish cells. After another week the little balls acquired more con- 

 siderable dimensions, and the number of bluish cells increased ; at the 

 same time these latter were found arranged in small doubled up chains, 

 of which some already contained heterocysts characteristic of Nosfoc. 

 Five weeks after the sowing colonies of perfectly formed Nosioc were 

 found, which consisted of numerous little chains, with completely 

 developed heterocysts ; the little chains were imbedded in a mucilage 

 bounded by very distinct outlines. The cultivation of the gonidia 

 proved therefore that they originated from the Nostoc, entirely changed 

 in form under the influence of the invasion of the hypha. 



Being desirous of knowing in what manner perfectly free Nostoc 



