435 



grate into a brown granular substance, and in this the yellow coloration 

 becomes more intensive. The upper surface of the leaf is often raised like 

 a wart when the tissue, rich in chlorophyll, is drawn into the abnormal 

 process of elongation. 



Frequently the progress of the disease is stopped when the elongated 

 cells become cork, then there are only yellow spots, recognizable when 

 im.mature, indeed, only when the light falls through them. The whole 

 centre of the disease may then be separated from the healthy tissue by a 

 zone of actual cork cells. As the disease advances in severity even the cells 

 of the vascular bundle sheath may be afifected and show the characteristic 

 elongation, brow^ning and swelling until finally the elongating mesophyll 

 cells rupture the epidermis above them. The processes already described 

 under the phenomenon of perforation now follow. Diseases due to fungi 

 and seemingly similar in outward appearances may easily be distinguished 

 in Pandanus, since in them there is no elongation of the cells. In Dracaena 

 rubra and Draco, the disease at times only disintegrates the chlorophyll of 

 the inner cell groups ; here membranes are often seen with bead-like swollen 

 places extending into the inner part of the cell. In studying Dracaena 

 indivisa, I observed an abundant formation of sugar in those tissues in which 

 the chlorophyll had dissolved. This sugar did not occur in healthy tissues 

 and disappeared from the diseased spots as soon as the walls began to turn 

 brown and develop cork. 



Hence this yellow spotted condition seems in many cases to be an 

 initial stage of real intumescence, in others, as in the Dracaena, it is usually 

 a diseased condition without any sequelae and the temporary increase of 

 sugar and the bead-like swellings of the walls point to causes which are 

 similarly affective in the over-elongation of the cells. In practical treatment, 

 one should realize that the plants exhibiting aurigo suffer from a supply of 

 water which they cannot assimilate. The amount of water destroying the 

 equilibrium need not be greater than that normally supplied, but, being given 

 during the dormant period, the plant cannot utilize it and the external con- 

 ditions are not such as could stimulate this absorption. The spots occur 

 with great frequency in the autumn and winter when the plants are brought 

 into a warm place. They then have sufficient heat, water and mineral 

 nutrient substances, but the light is deficient. Hence the one-sided stimulus 

 must be removed and the plant put in a cooler, dryer place where there is as 

 much light as possible. 



Intumescences. 



The knot-like or pustule-like distensions of the tissue usually occurring 

 in groups and which I have considered as "Tntumescentia" have not been 

 sufficiently studied by practical pathologists. They are most abundant in 

 leaves but are not rare on the stems. However, as yet. the observation of 

 intumescences on blossoms and fruits has been limited. 



The consideration of a specific case gives the best information as to the 

 development of such structures, the A'alue of which lies in their symptomatic 



