290 SUMMARY OF CURRENT RESEARCHES RELATING TO 



by Falkenberg; but the two first- named species produce also adven- 

 titious shoots of exogenous origin on the mid-rib of tbe thallus. The 

 facts are, therefore, precisely the opposite to those that occur in the 

 higher cormophytes, where the normal shoots have an exogenous, the 

 adventitious shoots an endogenous origin. A third species, Polyzonia 

 jungermannioides, which bears a remarkable resemblance in habit to 

 some species of Jungermannia, presents a somewhat different structure. 



Spiral Phyllotaxis in Florideae.* — Professor Schwendener has 

 investigated the regular spiral phyllotaxis of the lateral organs in 

 Polysrplionia, Spyndia, and other Florideae, for the purpose of deter- 

 mining whether it depends or not on the contact of the organ with the 

 next oldest one. 



In those species of PolysipTionia with the lateral organs in four 

 rows, viz. P. sertularioides, variegata, &c., the breadth of the rudiments 

 of the youngest leaves at the apex is about one-fourth of the circum- 

 ference of the stem ; which supports the theory of contact. The young 

 leaves are closely applied to the stem by their inner surface, and the 

 apices of the uppermost leaves invariably reach to the level of those 

 freshly formed. 



In PolysipTionia Brodiaei, the leaves (lateral organs) are arranged 

 in a |- phyllotaxis, and the relationship of the breadth of the rudiments 

 to the circumference of the stem is in correspondence. The pheno- 

 mena are the same in P. sertidarioides ; and in Clwndriopsis it is f . In 

 Spyridia filamentosa the arrangement is -f'^, and the structure the same 

 as in many flowering plants. As the segment-cells ai*e very short, 

 and each produces a leaf-rudiment, their hooked projections are 

 closely adpressed. These facts render it scarcely doubtful that the 

 occurrence of a spiral arrangement of the lateral organs depends on 

 the same causes as in higher plants. The same is the case in Acan- 

 thophora. 



Sargassum and the Sargasso Sea.f — Dr. 0. Kuntze gives the 

 following as the general results of a very careful examination of the 

 various points connected with the so-called " gulf weed," Sargassum 

 hacciferum. 



1. The diagnosis of the species by Linnfeus, Turner, and C. and J. 

 Agardh depends on a series of errors, and presents no constant 

 cbaracter by which it can be distinguished from S. viilgare. 



2. Very different forms have been described by later authors and 

 travellers as S. hacciferum, the reputed species being found only in the 

 floating state, and belonging to the most extreme species of the genus. 



3. The floating specimens consist entirely of broken-off upper 

 branches, which are mostly much branched, with numerous small 

 bladders, while the lower parts, which are less branched, have a few 

 large bladders, and, when old, are leafless, and entirely wanting in the 

 open sea. 



4. It is only the remains of old plants that are found floating, 



* j\IB. k. Prenss. Akad. Wiss., 1880, pp. 327-38. 



t Eiigler's Bot. Jahrbuch, i. (1880) pp. 191-239. See also 'Nalmv,' xxiii. 

 (1880) p. 70. 



