178 
Parasitic Aphelenchi 
Embedding in paraffin. The tissue should be transferred to chloroform, 
paraffin (60° C. m.p. for vegetable tissues) added to saturation, the chloroform 
slowly evaporated in an incubator for 24 hours. Transfer to two baths of 
melted paraffin for 5 and 10 minutes respectively. 
Staining sections. Thionin and eosin give the best results. 
SUMMARY. 
There are three species of true parasites in the genus Ajyhelenchus, viz.: A. 
fragariae R.B., 1891, A. olesistus R.B., 1893, and A. phyllophagus n.sp. 
A. ormerodis R.B., 1891, is a doubtful species, possibly a young form of A. 
fragariae (Marcinowski, 1908). 
A. fragariae causes the disease strawberry bunch; A. olesistus and phyllo¬ 
phagus cause leaf disease in flowering plants and ferns. The diseases are widely 
distributed and of considerable economic importance. 
From the study of the anatomy of the three species certain points of general 
importance emerge: (1) The salivary glands of Aphelenchus represent the 
oesophageal glands of other nematode genera, which have separated from the 
body of the oesophagus. This separation causes the reduction in size of the 
posterior portion of the oesophagus, and its lack of clear demarcation from 
the intestine. (2) The excretory organ of Aphelenchus, and of some other 
nematode genera, originates from the left lateral line. (3) The vaginae are 
ectodermal organs distinct in origin from the gonads proper. 
The life cycle of the parasitic Aphelenchi is divided into three definite 
stages: (A) That of residence in the definitive habitat, which for A. fragariae 
is in the stem and leaves of the strawberry plant, for A. olesistus and phyllo¬ 
phagus in the inesophyll spaces of the leaves of many plants. Nutrition and 
reproduction are most actively carried on in this situation, several or many 
generations succeeding each other, and here the pathological effects are mani¬ 
fest. (B) The resting stage in the soil. The worms reach the soil in fallen 
leaves, and the adults survive in a partially dried, dormant condition on the 
surface of the soil for prolonged periods. (C) The stage of immigration into 
the host plant. When revived by moisture the AjAielenchi may be attracted 
by a suitable plant, and wanders on to it; they may live as ectoparasites in 
the leaf axils, breeding in this situation, the larvae migrating to the definitive 
habitat; or they may enter the definitive habitat direct. They do not traverse 
the tissues of the stem during immigration. A. olesistus and phyllophagus 
enter the mesophyll spaces through the stomata. 
It should be noted that this life cycle is that of the race, not of the indi¬ 
vidual. It comprises many generations, and in this respect resembles that of 
Tylenchus dipsaci and differs from that of T. tritici, which includes one 
generation only. 
In the life of the individual Aphelenchus, embryonic development occupies 
not more than five days, embryonic and larval development not more than 
ten, and a complete generation not more than fourteen days. 
