THE GRANA 



359 



plasts of Mnium, Vallisneria, Cabomha, and MyriophyUum, as well as by 

 the observations of Wieler (193(3) on Elodea and Weier (1936) on more 

 than 100 species, particularly beet. Especially convincing were numer- 

 ous photographs reproduced in a second investigation by Heitz (1936), 

 in which the grana were observed and measured in the higher plants of 

 all classes — including cryptogams, monocotyledons, and dicotyledons. Some 

 of Heitz' photographs are reproduced in figure 39. His material did not 

 include algae. Earlier investigators have reported that algal chromo- 



^ 



Fig. 39. — Grana (after Heitz 1936). a. Agapanthus umbellatus, horizontal slice 

 through the spongy parenchyma; b. Selaginella Watsoniana, giant chloroplasts in intact 

 young leaflets of the sporophyll stalks, leaf surface cells; c. Todea superba, side view of 

 the chloroplasts; d. Sizes of grana in different species (drawing), the last one being in the 

 state of division. 



plasts are homogeneous. It is, therefore, important that Geitler (1937)' 

 and Hygen (1937) found that grana can be observed also in algae — even 

 the blue-green algae, which have no chromoplasts at all. True, Geitler 

 failed to discern grana in certain species of algae; but since the smallest 

 observed grana were close to the limit of microscopic visibility — about 

 0.3 p. — one could assume that, in these species, they fell below this limit. 

 However, grana are not equally clearly visible in the chloroplasts of all 

 the higher j)lants also. Some appear homogeneous under all conditions 



