1918] CURRENT LITERATURE 385 
mitochondria in that they are larger and rounded, while the mitochondria are 
very small granular or rod forms. Cells from the thallus of Amthoceros were 
studied because they have each a single chloroplast and hence furnish favorable 
objects for determining whether mitochondria are merely disorganized chloro- 
plasts. This -saention is answered in the negative. In Adiantum pedatum 
finds tl lria are small, granular, and rod-shaped. Discussion 
is here confined to root tips, and we are promised a subsequent paper dealing 
with other parts. The ‘“‘plastid primordia” are rounded, lenticular, and rod- 
shaped, but much larger than the ern = sstelerasetees “ primordia ” 
which do not develop into leucoplasts ‘‘ contin long-drawn-out 
threads and finally disappear.” In the younger growing parts of the stem of 
Pinus Banksiana numerous small rounded bodies with colorless centers (plastid 
primordia) and densely staining granules (mitochondria) were found. In the 
older parts these bodies with the colorless centers form the plastids, while the 
granular mitochondria have become larger or formed rod mitochondria. In 
the leaves of Elodea canadensis the primordia are rod-shaped and can easily 
be traced in their transformation into plastids. The mitochondria are very 
numerous, and in cells with fully developed chloroplasts they are globular and 
even rod-shaped, differing from the primordia only in size. We are promised 
a later paper dealing with his results on Hydrodictyon. 
GUILLIERMOND includes under the term mitochondria all those structures 
which give the same histochemical reactions, regardless of their functions; 
while Mortter, on the other hand, considers only those structures which do 
not develop into plastids to be included under the term. Both, however, 
agree that these structures are ‘‘morphological units of the cell with the same 
rank as the nucleus.” Mortrer goes farther and asks, ‘‘ What characteristics 
are transmitted solely by the nucleus, and what by the primordia of plastid 
and by the chondriosomes? There are many transmissible characteristics 
which cannot as yet be definitely expressed in any Mendelian ratio c 
that certain phenomena of fluctuating variations and other numerous charac- 
teristics, Mendelian or otherwise, owe their appearance and transmission to 
the primordia of plastids and chondriosomes may be a daring hypothesis, but 
if, as there is good ground to believe, tiene bodies are permanent organs, there 
is no escape from some such assumption.’’—Ray C. FRIESNER. 
Units of vegetation and their classification.—With the advance of the sci- 
ence of ecology there has been a gradual evolution of opinion as to the units 
most suitable for the analysis and study of vegetation. The earlier stages of 
this evolution have been well diseussed by Moss,’ who also advanced the devel- 
opmental concept of the plant formation. The half decade following this paper 
passed without a further notable contribution to the subject, but recently three 
7 Moss, C. E., The fundamental units of vegetation. New Phytol. 9:18—53. 
Igio, 
