SECT. I 



CRYPTOGAMS 



369 



This substance appears to be a carbohydrate, and, according to 

 Hansteen (•*^), originates in the chromatophores. Among the more 

 highly developed forms the thallus exhibits a highly differentiated 

 anatomical structure. The outer cell layers, as a rule, function as 

 an assimilatory tissue, the inner cells as storage reservoirs. In the 

 Laminariaceae and Fucaceae structures closely resembling the sieve- 

 tubes of the cormophytes occur, and jDossibly conduct albuminous 

 substances (^'''). 



Two orders of Phaeophyceae may be distinguished. The Phaeo- 

 sporeae are vegetatively reproduced by means of zoospores and 

 sexually by ciliated gametes ; they thus resemble Ulothrix among the 

 Green Algae. The Cyclosporeae show a marked differentiation of 

 their sexual cells into large, naked, non- 

 motile, spherical oospheres and small, 

 ciliated spermatozoids ; some forms are 

 also asexually reproduced by means of 

 naked, non-motile spores. 



Order 1. Phaeosporeae (^'^) 



In this order are included the Lamiuarias, as 

 well as the majority of the other Phaeophyceae. 

 Asexual multiplication is effected hy means of 

 swarm-spores, which are produced in large numbers 

 in simple (unilocular) sporangia ; they have a red 

 eye-spot, a chromatophore, and two laterally 

 INSEUTED cilia (Fig. 292), one directed forwards 

 and the other backwards. Only this asexual re- 

 production is yet known in the Laminariaceae. 



In addition to unilocular sporangia, multi- 

 locular sporangia are produced in the Phaeosporeae 

 (Fig. 293). Each cell of the multilocular sporangium 

 2>roduces a single swarm-spore, rarely several. The 

 conjugation of these swarm-spores has been observed 

 in some genera. On this account these swarm- 

 spores must be termed planogametes, and the corre- 

 sponding sporangia gametangia. The degree of sexual differentiation varies, and 

 in some cases the swarm-spores produced in multilocular sporangia can germinate 

 without conjugating, as was seen to occur in Ulothrix among the Chlorophyceae. 



Ectocurpus siliculosus (Fig. 294) will serve as an example of the mode of con- 

 jugation of gametes produced from multilocular gametangia. The gametes are 

 similar in form, but their different behaviour allows of their distinction into male 

 and female which are formed in distinct gametangia, borne on the same, or different 

 plants. The female gamete becomes attached to a substratum, and numerous 

 male gametes gather around it (Fig. 294, 1). Ultimately a male gamete fuses 

 with tlie female to form a zygote (Fig. 294, 2-9). This contains after the fusion 

 a single nucleus, but two chromatophoi'es, and soon becomes attached and 

 surrounded by a cell wall ; it gro^.•s into a new plant. 



In other Phaeo}ihyceae the distinction between the two kinds of gametes is 



2b 



Fiu. 292. — A, I'lenrucladia lacustris. 

 Unilocular sporangium with its 

 contents divided up into the 

 zoospores ; a, eye - .spot ; chr, 

 clironiatopliore. (After Kle- 

 BAHN.) B, Chorda filum. Zoo- 

 spores. (After Reinke.) (From 

 Oltmanns' Algae.) 



