on the Sporidia of Puccini a malvacearum (Mont.). 335 
was used, quite normal and vigorous germination resulted. The material 
of this species used had very few glandular hairs. 
A number of experiments was carried out in which the sporidia were 
sown upon the epidermis of short pieces of the petiole of leaves of Althaea , 
Pelargonium , and potato respectively. After three days the epidermis on 
which the sporidia rested was stripped off, fixed in alcohol, and either stained 
in erythrosin and mounted in glycerine or embedded and cut in serial 
sections. No normal germination was noted in the case of Pelargonium , 
the sporidia having behaved as in the cover-glass cultures. On the leaves 
of Althaea and potato, however, the germ tubes were normal and their tips 
showed a slight swelling which was pressed against the epidermis (Fig. 3). 
Fig. 3. Sporidia germinating on the epidermis of a fragment of the petiole of a potato leaf. 
Normal germination with a slight swelling at the tip of each germ tube pressed against the epidermis, 
but no penetration of the cuticle, x 300. 
No case of penetration of the epidermis by the germ tube was seen in the 
case of the potato, though on Althaea the tip of the germ tube had pene- 
trated the epidermis and formed an infection vesicle within the epidermal 
cell. This normal infection has already been described and figured by 
Kellerman, 1 Rathay, 2 Eriksson, 3 and myself. 4 
My attention was called to the negative heliotropism of the germ tubes 
by a preliminary experiment in which they appeared to be directed towards 
a fragment of leaf on the drop of gelatine. More critical examination of 
1 Sitzber. Phys. Medic. Soc., Erlangen, 1874. 
2 Ueber das Eindringen der Sporidien-Keimschlauche der P. malvacearum in die Epideimiszellen 
der Althaea rosea. Verh. k. k. Zool. Bot. Ges., Wien, 1881. 
3 Der Malvenrost. Kungl. Svenska Veten'sk. Hand., Bd. xlvii, 1911. 
4 On Some Relations between P. malvacearum and the Tissues of its Host-plant. Memoirs of 
the Manchester Literary and Philosophical Society, 1913. 
