96 Dr. R. Caspary on Furcellaria fastigiata 



Differences in the Structure of the Stem between Furcellaria fasti- 

 giata mid Polyides rotundus. 



1st. The epidermal outer stratum in Furcellaria fastigiata 

 consists only of two or three^ seldom more, layers of cells, which 

 are two to four times longer than broad ; breadth : length = 1 : 

 2—4. The epidermal outer stratum in Polyides rotundus consists 

 of 4-5, seldom so few as three layers of cells, which are nearly as 

 long as broad; breadth : length = 1 : 1 or nearly so. 



2Qdly. The third sort of cells arranged in strings have towards 

 the axis of the stem in Furcellaria fastigiata an almost perpen- 

 dicular direction or nearly so with little granular matter ; whilst 

 in Polyides rotuyidus they have a slanting direction towards the 

 axis of the stem, and contain in most cases many grains. 



Srdly. The fourth perpendicular sort of cells in the middle of 

 the stem is in Furcellaria fastigiata rarely filled with a granular 

 matter, cylindrical, not thicker at the junctures with the next 

 cells than in their middle ; the relative proportion of breadth : 

 length = 1 : 15-20 : whilst the corresponding cells m Polyides 

 rotundus contain in most cases much granular matter, have the 

 form of a femur, that is, are thicker at the junctures than in the 

 middle, and are shorter than the cells m Furcellaria fastigiata ; 

 breadth : length = 1 :8-15. 



These differences, particularly the first, will enable every accu- 

 rate observer to determine any portion of the stem of the two 

 plants, be it ever so small, if it only admits of transverse and 

 longitudinal sections. 



All these observations were made on vigorous plants which had 

 not been previously put into fresh water. Sea-water was em- 

 ployed under the microscope. Old decaying plants show many 

 differences in their structure. There will come a time when it 

 will be found necessary to give, in describing Algse, not only the 

 relative proportions of breadth and length of the cells, as is 

 already now partly done, but also the absolute size of them. 



I add at the risk, ut acta agam, the generic character of both 

 plants : — 



Furcellaria fastigiata. 



Frond cylindrical, dichotomous, cartilaginous, solid, fixed by 

 many small discs, which are either sent out from the base of the 

 perpendicular ones on the base of the perpendicular stems, or 

 here and there on small, horizontal, often branched stems. The 

 perpendicular stem composed of four sorts of cells, the walls of 

 which are colourless or slightly tinged greenish or brownish. 

 1st. The epidermal layer with brown grains attached to the 

 wall, cells horizontal : a, the outer part, consisting of 2-3 radia- 

 ting layers ; breadth : length = 1 : 2-4 ; average absolute size. 



