Effect of Spore Coalescence on the Early Development of Gracilaria verrucosa (Hudson) Papenfuss.

Abstract

CARPOSPORES and tetraspores of G. verrucosa have been grown on microscope slides in running, natural sea water under constant illumination. After the initial attachment to the slide, divisions occur which correspond, in general, with the observations of Killian¹. These produce, in 40–45 days, a dome of cells which may be 30–35µ high and 120µ in diameter. In the majority of isolated sporelings there is a great reduction in activity at this stage ; but in some cases development of the shoot begins, in circumstances described below. The peripheral growth of closely adjacent spores leads to their meeting and coalescing into irregularly shaped ‘rafts’. In these rafts individual sporelings cannot be recognized after a time unless their positions have been mapped at earlier stages. On all slides shoots have been first observed arising from rafts of this kind. Isolated sporelings, on the other hand, rarely show any change from the 40-day condition after several months, by which time coalesced sporelings of the same age have produced shoots several millimetres long. Shoots are not produced by all sporelings in a raft, and, when an extensive raft produces numerous shoots, these are well spaced out and seldom arise from adjacent sporelings. Furthermore, it will be seen from Fig. 1 that the larger rafts tend to bear proportionately longer shoots. On the slide concerned, the longest (1.8 mm.) occurred on a raft of about five sporelings. Larger rafts on the same slide bore more than one shoot, but none was longer. The largest raft, containing about fifty sporelings, bore ten shoots averaging 0.61 mm. in length, the longest measuring 1.6 mm. A ratio of five sporelings to each shoot seems usual in the larger rafts ; but the frequency of the small shoots produced on isolated sporelings is much lower than 1 in 5.