May 20, 1918 Chemistry and Histology of Glands of Cotton 42 1 



DEVELOPMENT OF INTERNAL GLANDS 



Internal glands, with the exception of those of the secondary cortex, 

 are developed from certain cells of the ground meristem. Those of the 

 seed are formed coincidentally with the development of the tissues of 

 the embryo, which are formed from the endosperm soon after fertiliza- 

 tion takes place. The process of gland development in all parts of the 

 plant, except the secondary cortex, is essentially the same. Within the 

 rapidly dividing tissue of the ground meristem a well-defined circle of 

 cells marks the boundary of the developing gland; the cells within this 

 circle are more or less concentrically placed (PI. 48, A). A marked 

 change of content takes place in the central cells; the protoplasm becomes 

 vacuolate and arranged in strands and is converted into a yellowish oily- 

 appearing substance (PI. 48, B, C). These changes are accompanied by 

 rapid swelling of the cells concerned, some of which are crushed and 

 obliterated in the process, while the peripheral layers become much 

 flattened. The nuclei of the swelling cells enlarge and soon degenerate 

 and disappear. The v/alls of the swollen cells usually are dissolved and 

 disappear rapidly, leaving the gland as a large central cavity surrounded 

 by layers of the flattened cells. In the seed glands (Pi. 42, C), however, 

 the interior walls never wholly disappear, but vestiges, easily dissolved 

 in water and probably of a mucilaginous nature, remain. The writers 

 regard the process of gland formation as truly lysigenous, for traces of the 

 secretion can be observed in the unbroken cells, and not, as the more 

 common schizogenous glands, first in the intercellular spaces, as figured 

 by Tschirch {ij, p. 1095-1268). 



While the secretion is first formed in the central cells, its general 

 solidification in the seed indicates that it may be added by the flattened 

 cells in the encircling layers, which then in their turn may act as secretory 

 cells, as in a schizogenous gland. The presence of this layer, usually 

 characteristic of the latter type of gland, is doubtless the cause for 

 Dumont's (2) reference to the glands of Gossypium spp. as schizogenous. 

 The cells of the encircling layers retain their nuclei and their walls at 

 length become considerably thickened. In the seed they are somewhat 

 mucilaginized, dissolving partially in water and cuprammonia, but not 

 in alcohol, and giving no well-defined cellulose reactions. In this latter 

 respect, however, they do not differ from the surrounding cell walls, which 

 are not water-soluble. 



The development of glands in the secondary cortex is similar, but 

 usually simpler. One or more cells may be involved in the process. 

 Upon their division from the cambium the nuclei quickly disappear, the 

 cells become filled with a dense yellowish oily substance, and enlarge 

 rapidly. When more than one cell is involved, the dissolution of the 

 dividing walls is more rapid than in the glands previously described. 

 The distension of the secretory cells flattens one or two surrounding cell 

 layers into an envelope resembling that of the primary gland. 

 49387°— 18 3 



