MORPHOLOGY 



til 



The Centrioles and Centrosomes. In a number of cases among 

 the lower Cryptogams (Thallophyta and Bryophyta) structures which 

 correspond to the centrioles and centrosomes of animal cells have 

 been demonstrated. Where centrioles are found, as in some marine 

 Algae (Fucus, Fig. 57), they are dumb-bell shaped. Larger masses of 

 active cytoplasm occur in a number of Fungi, and, though they do 

 not, like them, include centrioles, are comparable with the centro- 

 somes of animal cells. Similar structures occur in the mother-cells 

 of the spermatozoids in Bryophyta, Pteridophyta, and certain Gym- 

 nosperms ( 39 ). They are there termed blepharoplasts, and provide 

 the material for the formation of the cilia of the spermatozoids. 

 With the exception of the blepharoplasts no structures comparable 

 .with centrioles or centrosomes have been shown to exist in the cells 

 of the higher plants. 



The Chromatophores ( 4(l ). In the embryonic cells of the embryo 

 and of growing points, where the chromatophores (Fig. 56 ch) are 

 principally located around the nucleus, they first appear as small, 

 colourless, highly refractive bodies. They may retain the same* 

 appearance in older cells (Fig. Ill A, I), but in them they also 

 attain a further development, as CHLOROPLASTS, LEUCOPLASTS, or 

 CHROMOPLASTS. Since these bodies have the same origin they are 

 all included in the one term, CHROMA TOPHORKS. 



Chloroplasts. In parts of plants which are exposed to the 

 light the chromatophores usually develop into 

 chlorophyll bodies or chloroplasts. These are 

 generally green granules of a somewhat flat- 

 tened ellipsoidal shape (Fig. 63), and are scattered, 

 in numbers, in the parietal cytoplasm of the 

 cells. All the chloroplasts in the Cormophytes, 

 and, for the most part also, in the green 

 Thallophytes, have this form. In the lower 

 Algae, however, the chlorophyll bodies may 

 assume a band-like (Fig. 264 e), stellate or 

 tabular shape. 



In these cases the chloroplast often includes one or more 

 pyrenoids ; these are spherical protoplasmic bodies con- 

 taining an albuminous crystalloid, and are surrounded 

 by small grains of starch (Fig. 264). The ground sub- 

 stance of the chlorophyll bodies is itself colourless, but 

 contains numerous coloured granules, which are termed 

 OKAXA. These consist of an oleaginous substance, which 

 holds in solution green and yellow pigments. These 

 colouring substances may be extracted by means of 

 alcohol, leaving only the colourless plasmic substance of the chlorophyll body 

 remaining. 



The easiest way in which a solution of chlorophyll can be prepared, is to extract 

 the chlorophyll by means of alcohol from green -leaves that have been previously 



:. ".'!. Two cells from ;i 

 leaf of Funaria liygi'n- 

 metrica. cl, Chlompla.st.s; 

 a. nucleus, (x 300.) 



