PATHOLOGIC PLANT ANATOMY 375 



sugar beets continue their growth to abnormal thickness by the forma- 

 tion of ridge-like tissue excrescences composed of normal layers of tis- 

 sues which extend longitudinally. De Vries investigated a case where 

 new cariibial rings were formed outside of the latest ones of the first year 

 coincident with an arrestment of activity. Hottas incased roots of 

 Viciafaba in plaster casts pierced by holes. He found that by correla- 

 tive growth homooplastic excrescences filled the holes. 



Some kinds of homooplasias are characterized by the fact, that only 

 single tissue forms of an organ are developed unusually without the for- 

 mation of local excrescences by which means the histology of the organ 

 is altered. Increased demand upon a tissue may result in the formation 

 of abnormally abundant tissue and to this the name of activity homo- 

 oplasias has been given. Various experiments have been conducted in 

 the attempt to form mechanic tissue by putting an increased mechanic 

 demand upon plant tissues. The experiments of Kiister with sunflower 

 stems were negative, as also those of Wiedersheim with branches of 

 beech and ash, for he found no strengthening of the hard bast in his 

 experiments. He proved, however, an increase of stereids in the 

 strained branches of Corylns avellana. Vochting has shown that hori- 

 zontal stalks of the Savoy cabbage strained at the extremity by hanging 

 weights developed thickenings on the upper side of the branch. De 

 Vries has described an abnormal potato tuber in which through the need 

 of conduction of plastic substances the bundles of the tuber had devel- 

 oped to an extent unusual to the normal plant. The wood and bast 

 portions were both increased. Vochting's experiments with potato 

 tubers supplement those of de Vries; for he succeeded in interpolating 

 the potato tuber as an element in the potato plants grown from it and 

 succeeded in getting hyperplastically developed vascular bundles. 



Correlation homooplasias result when there is a local arrestment of 

 growth, and growth is started elsewhere with homooplastic changes in 

 the tissues. The experiments of Boirivant and Braun have proved this 

 in a number of plants. Only one case of callus homooplasia has been 

 reported and it is described by Schilberszy, who succeeded in stimulat- 

 ing an increase of vascular tissue in the stalks of Phaseohis mtdtiflorus 

 through injury. No positive cases are known where homooplasias 

 occur in the formation of galls. 



Heteroplasias. — This term of pathologic anatomy is used when 

 there is a quantitative increase of an organ in which by abnormal di- 



