128 



Ohlorophycew 



definite pores in the cell-wall. In the DesmidiaceaB it exhibits a distinct 

 radiating fibrillar structure. 



In many of the Green Algge there are various inorganic salts present 

 in small quantities in the cell-wall, and not infrequently traces of silica. 



Protoplasmic continuity between the cells of the thallus has not been 

 shown to exist in the multicellular Green Algaa, notwithstanding the pores 

 which are sometimes present in the cell- wall. In the Conjugatse the cells 

 of most of the filamentous forms are quite able to lead an independent 

 existence. 



There is a definite and well-differentiated NUCLEUS present in the 

 cells of all Green Algae ; but, of course, in the coenocytic forms, and in 

 the segments of the incompletely septate forms, there are many protoplasts, 

 and therefore many nuclei, within the confines of the cell-wall. In outward 

 shape the nucleus may be spherical, ellipsoidal or lenticular. The details 



.ki 



Fig. 88. Different types of zoogonidia. A, zoogonidium of Cladophora, x about 2000 (after 

 Strasburger) ; B, zoogonidium of Microspora xtagnorum (Kiitz.) Lagerh., y, 1000 ; C, zoogo- 

 nidium of Tribonema bombycinum (Ag.) Derb. & Sol., x 900 ; D, zoogonidium of a large 

 species of (Edogonium, x 800. ch, chromatophores ; ki, kinoplasm ; n, nucleus ; ol, oil 

 globule; pij, pyrenoid ; s, starch ; st. stigma (or pigment spot). 



of the nuclear structure are as yet very meagre, but, in general, the resting 

 nucleus presents a fine reticulum with a few thickenings at the angles of the 

 meshes. There is a conspicuous nucleolus in many cases, but this structure 

 may be somewhat irregular and compound, as shown by Lutman ('11) in 

 Closteriuni Ehrenbergii. Nuclei with several nucleoli have also been de- 

 scribed. In most of the Chlorophyceae the nuclei are very small, a fact 

 which materially increases the difficulties of their detailed study. The 

 general structure of the nuclei of the Chlorophycese thus far investigated is 

 essentially the same, and is not materially different from the nuclear structure 

 exhibited by higher plants (vide McAllister, '13). 



In all those Green Algae in which the nuclear structure has been studied 

 in detail the nuclear division has been shown to be mitotic. The genus 

 Spirogyra has received most attention in this respect, and Pfeffer has shown 

 that by etherizing the living cells the division could be changed from 



