191 



Plasmodesmen. 



By Frank Marion Andrews. 



It has been shown by W. Gardiner/ Strasburger,^ Kohl,- and others 

 that plasmodesmen are not confined to the pits in the cell walls but that 

 they may also penetrate the cell walls themselves at other places. Excel- 

 lent names for the plasmodesmen penetrating the cell wall in the places 

 above mentioned have been chosen by Kohl.^ Those which pass through 

 the pit membrane he calls aggregated and these which pass tlirough the 

 unpitted membrane solitary. Strasburger' has recommended for all these 

 protoplasmic connections the term plasmodesmen. It has also been shown 

 that the plasmodesmen arise independently of cell division, for in the 

 dermatogen of a plianerogam, in wliich only anticlinal and i-adinl walls 

 are formed these plasmodesmen are present in the walls between the der- 

 matogen and the next inner layer of cells. 



Tlie plasmodesuKMi arise, according to Strasburgcr, secondarily in a 

 very early stage in tlie lormation of the membranes, before the beginning 

 of their secondary thickening. Pfeffer" states — according to reports^ — that 

 a subsequent formation of very thin plama connections is just as possible, 

 as tlie larger fusion of protoplasts, which is made possible by dissolution 

 ■of adequate parts of the cell wall. 



I have investigated the occurrence of plasmodesmen to some extent 

 in the endosperm of Phoenix dactylifera. and find both the solitary and 

 aggregate forms present in large numbers. 



Fig. 1 represents a cross-section of a cell of the endosperm of this 

 plant before treating witli any reagent. The pits are large and numerous 

 and are generally somewhat enlarged Avhere the ends come together with 

 the corresponding ones of contiguous cells. The walls are rather thicli 

 and hard. Fig. 2 is a longitudinal section of the endosperm of Piioenix 



'Gardiner \V. Arbeiten des Botanischen Institute? in Wurzbiirg 1888, Bd. 3, p. 52. 

 ^'Strasburger Ueber Plasmaverbindungen pfianzlicher Zellen Jahr fiir wis. Bot. 1901, 



Band 36, p. 493. 

 =Kohl-Ber. d. Deutsch botan. Gesell=ch. 1900, p. 364. 

 ^Kohl-Ber. d. Deutsch botan. Gesellsch. 1900, p. 364. 

 ^Strasburger-Ueber Plasmaverbindungen pflanzlicher Zellen Jahr fiir wis. Bot. 1901, 



Band 36, p. 503. 

 ^Pfeffer-Pflanzenphysiologie zweite Auf. 1904, Bd. II, p. 219. 



