GROWTH, ETC., IN THE DESMIDIACE^. 293 



The growth of spines on the zygospore has ah"eady been 

 noticed ; they grow in the same manner on the cell. Spines, pro- 

 cesses, etc., often originate as puncta-spots in the membrane, cf. 

 Ralfs., xxi, f. 5i, where at the tip of the angles a faint spot is 

 delineated, an indication of the process afterwards found in St. 

 orbiculare var. ^erminosimi, and of the tooth in var. deniictdatiim, 

 Nord. (the senile form of orbiculare. cf. Nord. Cent. Braz., T. iv, 

 f. 42). The puncta-spots develop into puncta-granules, or denticu- 

 lations form, which grow out generally into a thin spicule, often 

 becoming bifid before expanding into a simple smooth bifid process. 

 This spinous growth occurs in Xan. hastifenim, Turn., in the four 

 apical spines most markedly. Entirely wanting in ft inevoUitum, 

 Nord., Frw. Alg. N.Z., PI. iv, f. 24, they have grown into minute 

 spicules in forma typica (Turner, Alg. E. Ind., t. xii, f. 25) and are 

 seen full grown in var. javanicum (Nord.), Turn., I.e., T. xii, f. 23. 

 I have found all these forms associated together in this country. 



Much the same process takes place in St. patens, Turn., in the 

 growth of the apical processes. First, a faint pustule or granule 

 (I.e., 1907, PI. V, f. 9), then a triangular tooth (var. planctoniciim, 

 G. S. West, Alg. Yan Yean, PI. 6, f. 14), next the tooth grows 

 into a stout spine (author's MS. figure) and the spine becomes a 

 smooth bifid process (I.e. 1908, PI. xiii, p. 11-12). The outer two 

 of the four processes in fig. 11 can be seen to be developing out of 

 a spine — the original point of the spine being bent outwards as 

 the other angle of the process forms. 



Similar development is found in St. sexangulare, Bulnh. The 

 young forms have onty one set of rays to the semi-cell, the rays 

 moreover to start with being almost smooth (var. stellinum, Turn., 

 I.e., 1907, PI. v, f. 11). The denticulations on the rays form first, 

 the rays getting stouter and shorter, var. piatycenim, Josh., I.e., 

 1910, PI. ii, f. 9. At the base of each ray a broad triangular tooth 

 then forms and grows first into a stout spine (var. dentatum, I.e., 

 PI. ii, f. 10) and then into a smooth bifid process (var. gemmescens, 

 I.e., PI. ii, f. 11). The latter lengthens, and denticulations gradually 

 form (var. suhglahrum, W. & G. S. West, I.e., PI. ii, f. 12), the ends 

 of the processes becoming 3 or 4-fid by growth of one or two extra 

 spines (cf. var. aspenim, I.e., PI. ii, p. 13). PI. ii, f. 10a shows an 

 alternative mode of changing from spine to bifid process. A 

 denticulation forms on each side of the spine ; these grow outwards 

 into aculei, the original point falls in and is drawn out flat. 



Attention has already been directed to the growth of processes 

 in St. orhicidare f . major ; its var. miiticum f . minor is also the basis 

 of a series of forms caused by the gradual development of similar 

 processes. This series includes all those forms hitherto gi'ouped 

 under St. montictdosnm, Breb. ; St. submonticidosum, Roy and 

 Bisset ; St. forficulatum, Lund. ; and St. aggeratum, Playf. The 

 cell is first quite smooth, then faint denticulations form (var. 

 granulosmn. I.e., 1910, PI. ii, f. 16), showing in vertical view as 

 faint granules. These develope into small triangular teeth in var. 

 aggeratum, Playf. (I.e., 1907, PI. iv, f. 21), and next into spines (var. 



