294 
THALLOPHYTES, 
is wanting in Nitella. From the basal node of each leaf one distinct cortical lobe 
runs downwards, and one upwards^ (Fig. 192, r, r', r", and Fig. 194). In the 
middle of each internode therefore as many descending cortical lobes as there are 
Fig. 192.— Longitudinal section througli a bud of Chara fragiiis ; in A the contents of the colls have been left out; in 
B the fine-grained substance is protoplasm, the larger granules are chlorophyll ; the formation of vacuoles is shown ; in C the 
contents of the cells have been contracted by iodine solution (x 500). 
leaves in the whorl meet with the cortical lobes that ascend from the whorl next 
below. The number of the latter is, however, smaller, because the leaf in the axil 
Fig. 193. — Leaves of Chara fragilis ; a terminal cell, b penultimate cell of a leaf; z internodal cell ; w cells of the leaf- 
node ; y" mother-cell of a leaflet and of its basal node : from it arise -v and 71 (the uniting cell), br basal node which 
produces four simple cortical lobes and ß the leaflet. A and C in longitudinal section, B an entire young leaf, external 
view, with the ' stipule' ^ and its descending cortical lobe sr ; D external view of the middle part of an older leaf, though 
still young ; E transverse section of a leaf-node, of the same age as D. 
of which the lateral branch arises does not form an ascending lobe. The cortical 
lobes are in close contact laterally, and form a closed envelope round the inter- 
^ The first internode of every branch and leaf becomes covered with a cortex derived only from 
the descending cortical lobes of the next node above. 
