OF BUCKLE YA QUADRIALA, B. ET H. 7 



but exceptionally oven a young one is enormously large ; for 

 example, I found on < 'rypiomcria a haustorium, only one year 

 old, which measured 8 mm. in diameter (Fig. 2 b), while, generally, 

 haustoria of such age measure only 3-4 mm. On the other hand 

 the largest haustorium which I have ever obtained was found on 

 Abie*: it had attained 14 mm. in diameter, at an age of perhaps 

 more than twenty years. 1 ' 



The surface of the haustorium is smooth when young (Fig. 

 5 a), but becomes gradually coarser, owing partly to the develop- 

 ment of the corky layer and its splitting off in scaly sheets as 

 in the epidermis of stem and root, and partly to the formation 

 of concentric stripes around the haustorium, which become more 

 numerous as the latter becomes older. 



In respect to their position on the mother-root, we can dis- 

 tinguish two kinds of haustoria — the lateral and the terminal. 

 The lateral haustoria occur most frequently and in the young 

 plant the haustoria seem to be exclusively of this kind, looking 

 like the nodules on the roots of Leguminosre (Fig. 1). However, 

 the haustoria in the older part of the root are generally terminal 

 and they make an appearance as if the root tips of the parasite 

 were penetrating directly into the * host-root (Figs. 2 b, c ; 3/; 4; 

 etc.). This difference in the position of haustoria leads us to 

 inquire their origin, their manner of formation and their mor- 

 phological nature. The occurence of a terminal haustorium in a 

 perennial parasite has been already noticed by Heinricher who 

 regarded this position in Lathrœa as being caused by the breaking 

 off of a part of the mother-root and added : " Ja, ich glaube auf 

 Grund eingehender Beobachtung sagen zu können, dass die Wurzel- 



1). The largest haustorium among Santalacea* was mentioned by Scott in the Santalum 



allium, as being 8 Unie (IS nun.) in diameter. Scott, loc. cit., p. 14S. 



