58 EMBRYOGENESIS IN PLANTS 



little information. In them the germinating spore divides, with a greater 

 or less degree of regularity, to form a basal cushion or attachment disc, 

 the centre of which grows out to form the thallus, Fig. 12u-w. The 

 data, which have been surveyed in some detail by Fritsch (1945), 

 indicate that the red algae do not all conform to one pattern in their 

 embryonic development. Accordingly, the group is one which is likely 

 to repay a closer examination. 



Oltmanns (1904) has described three types of development in the 

 group. Kylin (1917) has also described three types, including and 

 extending the Oltmanns types, as follows: (i) the germ-tube type, 

 found in the Nemalionales and some Cryptonemiales ; (ii) the attach- 

 ment-disc type, as in Gigartinales, Rhodymeniales and many Cryptone- 

 miales; (iii) the erect type, as in the Ceramiales. Chemin (1937), on 

 the basis of an extensive investigation, considers that it would be more 

 appropriate to recognise five types of young plantling. He would 

 retain the polarised or erect Ceramium-typQ as a well-defined configura- 

 tion. Contrary to the view of Kylin, he would retain the hemispherical 

 type of Oltmanns which Kylin had included in the attachment-disc 

 type; because of its similarity to the morula in animal embryogeny, 

 he suggests that it might be referred to as the morula type (type 

 moruleen) but he suggests the designation Dumontia-typQ. As to 

 Kyhn's germ-tube or filamentous type, Chemin considers that this in 

 reality comprises three types: (i) the Nemalioii-typQ, in which the 

 spore-contents move entirely into the germ-tube ; (ii) the Gelidium-typQ, 

 which is more accurately designated as an attachment-disc type; and 

 (iii) the Naccaria-type, in which the spore is not emptied of its contents. 

 Chemin notes, however, that while these five types show well marked 

 differences, they are in no sense absolute, intermediate types being also 

 known. He also observes that the adult form is seldon realised from 

 the outset: almost invariably it is preceded by a more or less charac- 

 teristic embryonic form — like the protonema in the development of a 

 moss. Without necessarily adhering closely to the so-called types, 

 some features in the embryogeny of various red algae may now be 

 briefly noted. 



In Nemalion multifidum. Fig. 12a-d, the essential features of 

 the germ-tube type of development are well seen. The carpospore 

 germinates to form a tube or filament into which all the spore-contents 

 pass, and a transverse wall is formed. The distal cell now elongates and 

 undergoes further divisions, and soon, or after some time, the lower- 

 most cell gives rise to a rhizoid. Similar developmental features are to 

 be seen in Batrachospermum and Lemanea among the Nemalionales, 

 in Grateloupia, Halymenia, Dudresnaya and Cryptonemia among 

 Cryptonemiales, and in Gelidium among the Gelidiales, (Killian, 1914; 



