EMBRYOGENESIS IN THE ALGAE 57 



and then several develop at a common point. When such a delay 

 occurs in Fiicus or Ascophyllum there may also be a development of 

 several rhizoids, or the single rhizoid may branch profusely (Farmer 

 and Williams, 1898). Kniep (1907) has described various anomalies in 

 the formation of rhizoids and in the initial segmentation of the zygote 

 in experimental and other materials. 



Parthenogenesis. Overton (1913) has reviewed the evidence relating 

 to parthenogenesis in the brown algae and has expressed agreement 

 with some earlier workers that this phenomenon is probably of rare 

 occurrence in Fucus. He has shown that some embryonic development 

 can be induced in unfertilised eggs by the experimental treatment used 

 by zoologists for eggs of various invertebrates. Batches of eggs of 

 Fucus vesiculosus, in which great care had been taken to exclude and 

 eliminate any contamination by spermatozoids, were placed for 1-5-2 

 minutes in 50 c.c. of water to which 3 c.c. of 0- 1 m of acetic, butyric or 

 other fatty acid had been added. In the course of 10 minutes many of 

 the eggs treated with acetic and butyric acids formed a membrane or 

 wall comparable with that of a fertilised egg. Most of the eggs con- 

 tinued to develop, became pear-shaped, formed a rhizoid, and under- 

 went segmentation within 24 hours, this being followed by other cell 

 divisions of the usual kind. In cultures which were kept properly 

 aerated, plantlings developed which were indistinguishable from those 

 resulting from normal zygotes. Overton has called attention to the 

 close parallelism between these developments in Fucus eggs and those 

 observed in the eggs of various marine animals. 



The cytology of the induced embryos was not investigated by 

 Overton, but he points to the interest that would attach to the rearing 

 of such plants to sexual maturity — unless, of course, a doubhng of the 

 chromosome number takes place at some point during the vegetative 

 development. 



RED ALGAE 



Although the red algae probably constitute a taxonomically coherent 

 group, the several subdivisions show considerable morphological 

 diversity and specialisation. Thus there are procumbent and erect 

 filamentous types, heterotrichous types, and uniaxial and multiaxial 

 types. In many species the young plants, whether originating from 

 carpospores, tetraspores or monospores, are characterised by a polarised 

 filamentous development. Figs. lE, f; 2c; 6a-d; 12. These organisms 

 have a further interest in that closely comparable, if not identical, 

 somata are formed from the diploid carpospore and the haploid 

 tetraspore. The developmental data for the more bulky uniaxial and 

 multiaxial forms raise special problems on which we have thus far 



