442 BOTANICAL GAZETTE [MAY 
During synapsis McAtuister finds that there is a lateral pairing and 
fusion of spirems, the fusion being complete at the time of the recovery from 
ynapsis. After this recovery there is a second contraction stage. The 
double heterotypic chromosomes are formed, not by the approximation of the 
limbs of loops, but by a transverse segmentation of a longitudinally split spirem, 
the line of the split probably representing the line of approximation of the two 
parental spirems seen at synapsis 
e heterotypic and lintestynle mitoses in the megaspore mother cell 
result in the formation of four megaspores, separated by plasma membranes 
The membrane formed at the heterotypic mitosis persists, while those formed 
at the homotypic mitosis quickly break down. From the inner binucleate cell, 
thus formed, an 8-nucleate embryo sac is developed. Consequently, two mega- 
spores are concerned in the development of the embryo sac. 
Adventitious embryos develop from nucellar cells in the micropylar region, 
and one or more of them may become mature. The presence of pollen tubes 
indicates that embryos may also result fot fertilization CHARLES J. 
HAMBERLAIN. 
Marine algae.—BorcEsEN” has published an account of the marine 
Chlorophyceae of the Danish West Indies, based upon collections made in 
1892, 1895, and 1905. The list contains 34 genera including 86 species, 4 new 
species being described in Cladophora (2), Avrainvillea, and Pringsheimia. The 
full field notes and the numerous illustrations make the account an exceedingly 
satisfactory one. 
BorGENSEN® has also given an account of the species of Sargassum col- 
lected during his three visits to the Danish West Indies, partly along the coasts 
of the islands, and partly in the Sargasso Sea. The shore collections include 
4 species, while the pelagic collections are all referred to two species. The 
discussion of the “biology, affinities, and origin of the gulfweed”’ is especially 
interesting. The conclusions reached are that the gulfweed of the Sargasso 
Sea consists of two species, S. natans (most common) and S. Hystrix, var. 
fluitans; that they are true pelagic algae, living perennially on the open sea; 
and that most probably they have descended from shore forms of the West 
Indies and the neighboring American coast. The author says “it is of great 
interest that we have an instance of floating, pelagic species of such a high alga 
type as Sargassum; because, as is well known, the higher types of algae are as 
a rule attached, and if detached they perish sooner or later.” —J. M. C 
™ BORGENSEN, F., The marine algae of the Danish West Indies. Part I. Chloro- 
phyceae. Dansk Botanisk Arkiv 1: ‘no. 4. pp. 158. figs. 126 and chart. 1913. Copen- 
hagen: H. Hagerup. Kr 4. 
3 , The species of Sargasswm found along the coasts of the Danish West 
ks upon the floating forms of the Sargasso Sea. Mindeskrift for 
Japetus Steenstrup. pp. 20. figs. 8. 1914. 
