362 



BOTANY 



PART II 



complicated, and the sperinatozoids are produced in so-called dwakf males. These 

 are short filaments (Fig. 282, C, a) consisting of but few cells, and are developed 

 from asexual swarm-spores (androspores) which, after swarming, attach them- 

 selves to the female filaments, or even to the oogonia. In the upper cells of the 

 dwarf male filaments thus derived from the androspores, spermatozoids are pro- 

 duced which are set free by the opening of a cap-like lid (Fig. 282, D, a). 



The genus Coleochaete (^^) is also oogamous. The long colourless neck of the 

 flask-shaped oogonium opens at the tip to allow of the entrance of the spermatozoid. 

 The spherical oospore increases in size and becomes surrounded by a single layer 

 of pseudo-})arenchymatous tissue derived from filaments that spring from the 

 stalk cell of the oogonium and neighbouring cells. In this way a fruit-like bodj' 

 is formed. On germination the oospore undergoes a reduction division and divides 



Fio. 282. — A, B, Oedogoninm : ^, escaping swarm-spores ; iJ, free 

 .swarm-spore. C, D, Oeilogonium ciliutum : C, before fertilisa- 

 tion ; D, in process of fertilisation ; o, oogonia ; a, dwarf 

 males ; S, spermatozoid. (After Princsheim, x 350.) 



Fig. 2S3. — BuUmchaete inter- 

 media. A, Oospore; B, 

 formation of four swarm- 

 spores in the germinating 

 oospore. (After Princs- 

 heim, X 250.) 



into 16-32 wedge-shaped cells, then breaks up and liberates a swarm-spore from 

 each Cell. 



Order 4. Siphonocladiales. — The Algae of this order are filamentous and 

 usually branched ; tliey are distinguished from the Ulotrichales by their large 

 multinucleate cells, the chloroplasts of which are either solitary, large and reticu- 

 lately formed, or appear as numerous small discs. 



The genus Cladcqihora, numerous species of which occur in the sea and in fresh 

 water, is one of the most important re}>resentatives of the order. CI. glomerata 

 (Fig. 284) is one of the commonest Algae in streams, often attaining the length of 

 a foot. It is attached by rhizoid-like cells, and consists of branched filaments with 

 typical a])ical growtli which some other representatives of the order do not show. 

 The structure of tlie cells is represented in Fig. 60. Branching takes place from 

 the upper ends of the cells by the formation of a protrusion which is cut off as the 

 first cell of the branch. Ase.xual rei)roduction is by means of biciliate zoospores 

 (Fig. 284), which arise iu numbers from the upper cells of the filaments, and escape 

 from these sporangia by a lateral opening in tlie \\all. The se.xual reproduction is 

 isogamous as in Ulotltrix. 



Only in the genus Sx>haeroplea has the se.xual reproduction become oogamous. 

 S. annulina consists of simi)le filaments and occurs in fresh water. 



ilany forms occur in the sea {e.g. SipliO)wcladus), and some have a jjighly 



