^170 



The Canadian Field-Naturalist 



[Vol. XXXVI 



buted by birds. Many birds come here in spring 

 and return south in the fall when the fruits are 

 ripe. There seems little likelihood of the seeds 

 having been brought from the south, as the birds 

 leave the southern climes before the trees have 

 come into flower. We have therefore to know 

 which birds eat the fruits of those trees and to 

 ascertain if such birds are migratory. 



This is a comparatively new branch of our work, 

 and its importance is rapidly gaining ground. It 

 means an examination of the crops of birds at 

 different seasons, and is of value to ornithologists 

 interested in the feeding habits of birds. As an 

 aid to this work we have in the University a 

 collection of seeds of nearly 1000 native plants. 

 We have most of the common species and many 

 of the rarer ones. 



While speaking of the inter-relationships of birds 

 and plants I should emphasize the fact that when 

 birds feed on berries and act as agents in the 

 dispersal of seeds they are not to be regarded as 

 parasitic. When a plant or an animal obtains its 

 food from another living plant or animal to the 

 detriment of the host, it is a parasite; therefore 

 when birds eat the cherries or the strawberries in 

 your garden they are rendering a service instead 

 of doing an injury to those plants. 



Struggle Between Plants and Animals 



It is different in the spring, however, when you 

 have sown sweet peas, and just as you see the 

 rows of little shoots appearing through the surface 

 of the ground, pheasants or other birds come along 

 and cause the seeds to come up faster than nature 

 intended they should. Birds may then be 

 regarded as biological parasites because their 

 feeding is detrimental to the host. Farmers and 

 gardeners frequently apply other terms to those 

 birds; but, from the omission of such terms from 

 our dictionaries, we may assume that they are 

 superfluous. 



The relationship of Botany to Entomology is 

 perhaps closer than that of any other branch of 

 Zoology; no one can become an efficient botanist 

 without some knowledge of Entomology; neither 

 can one become an efficient entomologist without 

 some knowledge of Botany. 



Two or three years ago I showed you how man's 

 interference with natural conditions around Van- 

 couver caused a change in the flora, with a con- 

 sequent change in the fauna, including the plague 

 of tent-caterpillars. Entomologists, working on 

 this problem from a purely entomological point of 

 view, had only one remedy spraying which] 

 was no remedy. The plague increased the follow- 

 ing year because the food plants were protected] 

 for the next generation of caterpillars. It wasi 

 not until the problem was tackled from the com-1 



bined entomological and botanical points of view 

 that an effective remedy was inaugurated; and 

 the destruction of food plants on vacant lots and 

 waste ground soon made an impression on the 

 plague and reduced the menace to our garden 

 crops. 



PlantJDiseases Caused By Animals 



Most of you are aware that the tent-caterpillar 

 is the larva of a moth, and I think all of you are 

 familiar with the devastation brought about by 

 its ravages; but we may be thankful that, so far, 

 we have escaped a plague of saw-flies. During a 

 short holiday in the State of Washington this fall, 

 I saw many Alder trees absolutely stripped of 

 every leaf, with myriads of small, green, smooth- 

 skinned caterpillars all over the trunks and bran- 

 ches; the ground under the trees was strewn with 

 hundreds of thousands of the wriggling creatures 

 with the characteristic coiled posterior end. In 

 one locality, about half way between Seattle and 

 Tacoma, we stopped for lunch at an auto-campers' 

 picnic ground. There were several large tables 

 set out for the use of campers in what was once a 

 beautiful grove of large Alder trees; at the time of 

 our visit they were practically leafless. You have 

 probably heard the expression "Raining cats and 

 dogs"; it was literally raining caterpillars. You 

 could scarcely find room on the tables to set a 

 cup down; in some places the caterpillars lay in 

 small heaps; if you wiped off a table with a news- 

 paper you had to do it carefully because the cater- 

 pillars were so easily squashed; and in the pitter 

 patter of falling caterpillars you were fortunate if 

 one did not fall on your sandwich or in your tea. 

 If this pest ever reaches our locality where we 

 have so many hundreds of thousands of Alder 

 trees we will have a plague many times more 

 disgusting than the one through which we have 

 passed. 



It is true that for purely local application spray- 

 ing may be effective in protecting individual trees 

 from the ravages of such pests, but it is useless in 

 combatting a plague. 



There are many diseases of plants caused by 

 insects and other animals which can not be reached 

 by sprays. I refer to those parasitic ani.nals 

 which cause malformations, tumours or galls on 

 roots, stems or leaves of plants. The study of 

 plant-galls and their makers necessitates an 

 intimate knowledge of plant physiology and histo- 

 logy, combined with a knowledge of the life history 

 and habits of certain groups of animals, particu- 

 larly mites, and some orders of insects. Nema- 

 todes frequently cause galls on roots, but as these 

 .are underground they are rarely seen. Any one, 

 [however, with open eyes will find a great variety 

 [of plant galls in this vicinity. 



