GuilHermond - Atkinson . — 44 — Cytoplasm 



the vegetative structure, varying according to the cells in which 

 they are found. They are irregular, or angular, disc-shaped bodies 

 or twisted ribbons. Moreover, chlorophyll is lacking in the rhizoids 

 and sexual organs. 



In the Charophytes there is little chlorophyll in the apical cell 

 and small ovoid chloroplasts are often found there containing a 

 large number of starch grains. In this group also, chlorophyll is 

 lacking in the egg and in the antherozoids. 



In the bryophytes, the chloroplasts are numerous and similar 

 to those of the phanerogams. Yet in Anthoceros there is only one 

 crescent-shaped chloroplast per cell, situated near the nucleus. It 

 is transmitted by division from cell to cell. 



It is therefore clearly proved by the study of algae such as the 

 Conjugatae where the chloroplasts are present in all cells, are 

 voluminous, and number only one or two per cell, that these organ- 

 elles are transmitted from cell to cell beginning with the egg. 

 However, their behavior during fertilization is not yet very clear, 



for it is very difficult to observe them in the 

 zygote. In the Desmidiales (Closterium and 

 Cosmarium) , in which the cells contain two 

 chloroplasts, Klebahn has stated that they fuse 

 two by two in the zygote. Nevertheless, it is 

 difficult to accept this supposed fusion, for it 

 has never been observed in other cases. In 

 another Desmid, Hyalotheca dissiliens, in 

 which the cells have only one chloroplast, it 

 seems well established by the recent work of 

 PoTTHOFF that one of the two chloroplasts, de- 

 — A Dividin ^ived from each of the gametes brought to- 

 chioropiasts in 'leaT cells gether in the zygote, begins to degenerate and 

 of Eiodea canadensis. B. (jigappears vcry rapidly. This is likewise re- 



Final stages in division *^^ ./!;'»' x rz J? 



of one chloroplast. ported for other Conjugatae. In Zygnema, tor 



example, where there are two chloroplasts in 

 each cell, four are found in the zygote (P. A. Dangeard and KuRS- 

 SANOW) and it seems well established by the work of Kurssanow 

 on Zygnema stellinum that the two chloroplasts carried by the 

 male gamete soon degenerate. This is also reported for Spiro- 

 gyra crassa (Chmielevsky) , S. longata and S. neglecta (Trondle) . 

 In the Conjugatae the chloroplasts of the new individual would 

 then have an exclusively maternal origin. In some algae, how- 

 ever, the sequence of events may be otherwise. In a diatom Rho- 

 palodia, for instance, each cell encloses a single chloroplast with 

 two pyrenoids. The cells destined to form the gametes divide in 

 their interior to form two gametes each. Now it appears that 

 the single chloroplast divides to furnish each gamete with half 

 a chloroplast possessing a single pyrenoid, because in the zygote 

 the two half-chloroplasts resulting from the union of the 

 gametes fuse to form a single chloroplast with two pyrenoids 

 (Klebahn). 



