CRYPTOGAMS 365 



infolded walls (shields). From the centre of each of the shields a large cylindrical 

 cell (manubrium) projects into the central cavity, and the inner end of this bears 

 a number of head -cells. The latter bear long septate filaments from each cell 

 of which a spirally wound biciliate spermatozoid is formed. The form of the 

 spennatozoid (Fig. 98 A) differs considerably from that of other Algae. 



The egg. after fertilisation, now converted into an oospore, becomes invested 

 with a thick, colourless wall. The inner walls of the tubes become thickened 

 and encrusted with a deposit of calcium carbonate, while the external walls of 

 the tubes soon become disintegrated. 



In a few cases, e.g. Chara crinita, the ovum can develop parthenogenetically 

 without being fertilised. Only female examples of this plant occur in Europe. 



The oospore, on germination, gives rise first to a simple, filamentous row of 

 cells, the proem bryo. From the first node of the proembryo rhizoids are produced, 

 while at the second node there arise, together with a few simple lateral axes, one 

 or more main axes, which finally develop into a full-grown plant. 



The formation of tuber-like bodies (bulbils, starch-stars) on the lower part of 

 the axes is characteristic of some species of the Characeae. These tubers, which 

 are densely filled with starch and serve as hibernating organs of vegetative repro- 

 duction, are either modified nodes with much -shortened branch whorls (e.g. in 

 Tolypellopsis stelligcra, when they are star -shaped), or correspond to modified 

 rhizoids (e.g. the bulbils of Chara ospera). 



CLASS XI 

 Phaeophyceae (Brown Algae) (> 20 ' 37 ) 



The Phaeophyceae, like the Chlorophyceae, can be derived from 

 unicellular Flagellata, and in particular from the Chrysomonadinae 

 which possess yellow chromatophores. On to these may be connected 

 unicellular colonial forms like Phaeococcus, or forms like PhaeotJiamnioit 

 composed of a short filament. The reproduction of these by means 

 of zoospores and conjugating gametes already agrees with that of 

 the simpler Brown Algae. 



With the exception of a very few fresh -water species, the 

 Phaeophyceae are only found in salt water. They are all attached, 

 and attain their highest development in the colder waters of the 

 ocean. They show great diversity in the form and structure of their 

 vegetative body. The simplest representatives of this class (e.g. the 

 genus Edocarpus) have a filamentous thallus consisting of a branched 

 or unbranched row of simple cells. Some Phaeophyceae, again, have 

 $. cylindrical, copiously branched, multicellular thallus (e.g. Cladotttephvs, 

 whose main axes are thickly beset with short multicellular branches 

 (Fig. 7) ; while in other cases the multicellular thallus is ribbon-shaped 

 and dichotomously branched (e.g. Didyota, Fig. 8). Growth in length 

 in both of these forms ensues from the division of a large apical cell 

 (Figs. 7 and 132). Other species, again, are characterised by disc- 

 shaped or globose thalli. 



