14 Robinson, Puccinia malvacearum and its' host plant. 



the haustorium is generally situated at the junction of the 

 two branches and the neck. Three or more such haustoria 

 often enter a single cell, and frequently a branch of one 

 reaches the nucleus {PL /., Fig. 13). Haustoria approach- 

 ing this form were also observed in the elongated cells of 

 the collenchyma and in the phloem of the leaf This 

 difference in form is quite possibly a modification due to 

 the elongated character of the cells entered. No haustoria 

 were observed in the sieve tubes, though hyphai occa- 

 sionally pass into the tracheids, but do not grow for any 

 distance along them and have not the form of haustoria. 

 In no case were haustoria observed to grow further, but 

 they appear to serve as definite absorbing organs of 

 limited growth. They differ, in this respect, from the 

 infection vesicle, branches of which grow out of the cell. 

 In the case of the cells of the leaf, it was only found 

 possible to study the earlier stages after entry by haus- 

 toria. PL II., Fig. 14, shows a normal cell of the spongy 

 mesophyll of the leaf, whilst in PL II, Fig. 15, a single 

 branched haustorium has entered such a cell, and lies in 

 the protoplasm with the tip of one of its branches in con- 

 tact with the nucleus. The nucleus is somewhat enlarged 

 and most of its chromatin has disappeared. The chloro- 

 plasts at this stage were to all appearances perfectly 

 normal, and this was also the case in the living material 

 examined {PL 11, Fig. 16). 



In living material of the petiole examined by means 

 of thick hand sections it is possible to observe that 

 in the case of the uninvaded cells of the cortical paren- 

 chyma, the nucleus is generally peripherally placed in the 

 cytoplasm which lines the cell wall and surrounds a large 

 central vacuole {PL II., Fig. 20). A number of chloro- 

 plasts lie regularly disposed in the cytoplasm. A young 

 haustorium entering such a cell {PL 11, Fig. 21) lies in 



