434 



As a phenomenon related to cork excrescences, I once observed wings 

 on young grape leaves. These appeared between the larger side veins on 

 the leaf blade and were opposite each other like lips. These outgrowths 

 (emergences) were a development of the blade usually forming over a 

 vascular bundle. 



The chagrinisation ((irannlation) of the rose stem should be cited here 

 in addition. As is well known, standard roses are laid flat through the 

 winter and covered with brush or earth. At times in the spring when 

 these are raised from the soil, the young bark stems, which should be 

 smooth, are often found covered with small warts, many having, as a rule, 

 a pale or brownish-red periphery. The warts are outgrowths of the lenticel. 

 These begin below the stomata and force the guard cells apart. Mycelia 

 may be proved to be present if the peripher}' is discolored. 



Yellow Spots (Aurigo). 



At times the leaves of monocotyledons, more than those of dicotyledons, 

 are covered with yellow or reddish brown specks. This speckled condition 

 begins at the tip. The specks usually shade through a pale green zone into 

 the otherwise normally green leaf. Their number may be increased, since, 

 as the disease progresses, small new specks are formed between the older 

 ones. At times the tissues afifected in the discoloration are forced out, 

 which shows a clear transition to real intumescences^ 



This yellow spotting occurs especially in greenhouse and house plants. 

 and among these, we find it most frequently in Dracacnae, palms and varie- 

 ties of Pandanus. 



To illustrate the formation of these specks and show how. under certain 

 circumstances, they increase until the leaf is perforated, I will cite some 

 observations on Pandanus javanicus. 



The spots always begin in the part of a mesophyll lying between two 

 veins. Toward the upper side of the leaf these cells resemble the palisade 

 parenchyma, on the under side, spong}' parenchyma, but in the centre they 

 are very thin walled, approximately isodiametric, somewhat hexagonal, 

 filled with a colorless water}^ content. 



From the innermost colorless tissue groups, the peripheral cells, i. e.. 

 those bordering on the mesophyll, containing chlorophyll, begin to stretch 

 excessively toward the side of the least resistance, viz., toward the centre, 

 whereby they frequently compress the central cells. Frequently the elon- 

 gation takes place only in the cells arranged directly upward and downward, 

 but not in the lateral ones of the thin-walled group, and a peculiar arrange- 

 ment is thus produced. The central part of the tissue then consists of empty 

 cells arranged radially, elongated like pouches, which often have become 

 thick-walled by swelling, later browning and turning to cork. With 

 increasing intensity, the spongy parenchyma is involved in this process of 

 elongation with the dissolving of its chlorophyll body; its contents disinte- 



1 Vol. 9, Part 5. 



