48 BOTANY 



are chiefly composed of a substance (Linin) which does not easily 

 take up the various stains employed in studying the nucleus. Im- 

 bedded in the linin-thread are more or less numerous granules, 

 composed of a substance (Chromatin) which is remarkable for its 

 avidity for staining-agents. The number and size of the chromatin 

 granules vary much at different times. One or more nucleoli are 

 generally present. These are usually globular, highly refractive 

 bodies, which stain freely with certain reagents, but differ from 

 the chromatin bodies in the color they assume. During the process 

 of cell-division the nucleolus disappears, but just what becomes of 

 its substance is not entirely clear. 



Blepharoplasts. Closely resembling in appearance the centro- 

 somes, are special structures known as Blepharoplasts, which occur 

 in the later stages of development of the spermatozoids of Ferns and 

 other related forms. From the blepharoplast are developed the cilia 

 with which the spermatozoid is furnished. There has been some 

 discussion as to the nature of the blepharoplasts, one suggestion 1 

 being the possibility of their being in some way connected with the 

 nucleolus. As the nucleolus is absent from the nucleus, which 

 becomes transformed into the spermatozoid, it is possible that the 

 blepharoplast may be composed of nucleolar substance which has 

 been ejected from the nucleus into the cytoplasm. 



Chromatophores 



In the cells of all green plants there are always found the chro- 

 matophores or plastids, which are wanting in the cells of Fungi. 

 These bodies are of three kinds Chloroplasts, Chromoplasts, and 

 Leucoplasts. The first are the green corpuscles containing the 

 green pigment chlorophyll ; the second, the red and yellow^cor- 

 puscles found in many flowers and fruits ; the latter, the colorless 

 plastids, including the so-called Starch-formers. 



In the young cells of the growing-point of a stem, or in young 

 spores, the plastids appear as minute granules, usually in the vici- 

 nity of the nucleus. They may sometimes be observed undergoing 

 division, by means of which their number is increased. As the 

 cells grow, the plastids increase in size, and they may develop chlo- 

 rophyll, or later assume a red or yellow color. In cells which are 

 not exposed to the light the plastids remain colorless, but these 

 may on exposure to light develop chlorophyll, and thus change into 

 chloroplasts. 



Chloroplasts are with few exceptions e.g. prothallium of Pilu- 

 laria, cotyledons of Pinus, young embryo of Celastrus produced 



i Fischer (3) , p. 247. 



