294 



THALLOPHVTES. 



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 fragilis ; in A the contents of the cells 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 



A"^ 



Fig. 193.— Leaves of Chara frag ill's; a terminal cell, * penultimate cell of a leaf ; z internodal cell ; 7u cells of the leaf- 

 node ; y" mother-cell of a leaflet and of its basal node : from it arise tj and tc (the uniting celt), br the basal node which 

 produces four simple cortical lobes and j8 the leaflet. A and C in longitudinal section, B an entire young leaf, external 

 view, with the ' stipule' j 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. 



