Crosby : OBSERVATIONS ON DICTYOSPHJERIA. 65 



than seven or eight) which compose them. These vary some- 

 what in number, have an irregular course and protrude to form 

 haptera and needles. 



Chemical tests did not show the sphaero-crystals that Murray 

 found in five Caulerfas^ but not in some Valoniacese also tested. 

 The walls are very refractive and present a finely wrinkled 

 appearance on the inner surface, which is not understood. 



Inner cell strengthening. Murray refers to "centripetal 

 membrane point thickenings " in six species of Caulerpa. These 

 have been reported only in leaves of Caulerpa, rhizoids of Mar- 

 chantia and cells of Dictyospharia. They are merely invagi- 

 nations of approximately three-fourths of the wall stratifications, 

 into the cavity of the cell at right angles to its depth (PI. XV., 



Fig. 5)- 



These needles are formed from the greater portion of the 

 wall and probably softer stratifications. They are refractive, 

 unseptate, colorless, thin-walled and with a waved -outline (PL 

 XV., Fig. 7). The same, of similar structure and develop- 

 ment, occur in Caulerfa, but differ in being branched many 

 times and interlaced. The present forms are found rarely 

 branched, with either basal (PL XV., Fig. 8) or apical dichot- 

 omy (PI. XV., Fig. p), yet they can be considered as allied in 

 function, and as a primitive condition of the well-developed 

 cross beams of Caulerpa. 



Their development occurs as follows : From a minimum (PL 

 XV., Fig. 6) an increasing number of stratifications invagi- 

 nate, the inner forming the external wall of the needle. The 

 next stratification passes within this, and this process continues 

 until a varying number have invaginated. Thus the stratifica- 

 tions appear as cross bars, with a lumen between, and a lumen 

 at the base of the needle, the space between the invaginated 

 stratifications and the remaining wall stratifications (PL XV., 

 Figs. <5-p). The plates explain further details and size. A 

 cross-section proves the theory. The needles occur irregularly 

 over the entire inner surface of the cells of a mature plant, ex- 

 cept the upper surface of external cells and the base of rhizoids, 

 where they are absent. The younger plants possess fewer, as 

 there is less strain. From the similarity in structure, origin and 

 branching they can in function be allied to the strengthening 

 structures in Caulerpa, which from its large cells needs both the 

 branching interlaced needles and interlaced branches of thallus. 



