HARD WICKE'S SCIENCE- G OSS IP. 



27 



captured them, by suddenly darting behind a tree, 

 when the snake would uncoil, and striking its tail 

 into the tree, would be held by it, and when in this 

 position would be killed by the person pursued. 



Now, all of these statements are just as explicit as 

 the finding of dormant swallows in the mud ; yet one 

 and all are absolutely false. If, therefore, the 

 impression is made on the minds of the young people 

 of any community that swallows hibernate in the 

 mud, it will be difficult to rid them of the idea that 

 any swallow that may be found in, or even near water, 

 is not indicative of their early teaching's truth, that 

 swallows do really pass the winter in such a manner. 

 Is this more unreasonable than that the belief in 

 hoop-snakes should be so common, even among other- 

 wise well-informed people ? If we cannot explain 

 this impression that swallows hibernate in mud, and 

 beneath water too, in some such manner as I have 

 endeavoured to make plain, there is left but one 

 other alternative, to exclaim, in despair, "Lord! 

 Lord ! How this world is given to lying." 



Let us turn now to a less abundant, but no less 

 interesting species, the cliff swallow. This bird, 

 instead of burrowing into a bank, builds an elaborate 

 nest of mud under the eaves of barns, along rocky 

 ledges, and, in New Jersey more frequently than else- 

 where, on the beams supporting the floors of bridges. 

 Proximity to the water is desirable, evidently, but is 

 not an essential condition of the locality chosen for 

 their nests. As in the case of the bank swallow, 

 these swallows live in large communities, and present 

 much the same general features of swallow-life. 



The peculiarity of their nest, in being made of mud, 

 of course necessitates frequent visits to water, whence 

 they derive this material for their nests. Now, unlike 

 the bank swallow, the cliff swallow is a late arrival, 

 and no sooner here, tired as he must be, than he 

 commences the work of nest building de novo, or of 

 repairs to the old homestead. In either case one 

 thing is absolutely necessary ; he must dabble in the 

 mud. Day in and day out, for a week or more, his 

 whole time seems spent in mixing mortar by the 

 water's edge, and transporting it in little bits to the 

 nest. He is wet and bedraggled much of the time ; 

 and if a cold north-easterly rain sets in, as is so 

 often the case the first week in May, then these 

 swallows are in a sorry plight indeed, and suspend- 

 ing building operations, huddle about in thickset 

 numbers, twittering mournfully, on the principle 

 that misery loves company. Such storms even some- 

 times prove fatal to many of them ; and they are 

 more frequently found dead near their nests, than are 

 individuals of any other species. Find them then 

 during a storm, or even notice them, for the first 

 time, when they are sitting on the ground at the 

 water's edge, dripping wet at times, and the impres- 

 sion you will have will be that of Kalm, that they 

 look " as if they had been just come out of, the sea." 

 This impression too is increased from the fact that 



there are no heralds of the northward moving mass 

 of swallows of this kind. One and all, they come 

 together. Yesterday, not one was to be seen ; to-day, 

 the entire community are settled in their old haunts, 

 and ready for house-keeping. Their migrations are 

 continued through the night, and either by starlight 

 or moonlight, as the case may be, they are guided to 

 their several haunts of the preceding summer. I am 

 very positive that they arrive during the night, and 

 I lay unusual emphasis on this fact ; because J:he ap- 

 pearance of such a flight of swallows the morning 

 following their arrival would be one to give an im- 

 pression of aquatic hibernation, if such an idea had 

 ever been expressed in your hearing. Not the entire 

 colony will immediately seek the nests of the past 

 summer ; there will be many young birds who have 

 as yet not built nests, birds yet to choose their mates. 

 Now such birds will sit in long rows on telegraph 

 wires, on fences ; and if it be near, be very sure that 

 they will congregate about the water. Seen, thus 

 congregated about a pond early in the morning, 

 perhaps after a heavy dew, and you can readily see 

 that they will be "as wet as if they had been just 

 come out of the sea ! " 



[To be continued.) 



NOTES FOR SCIENCE CLASSES. 

 Part V. 



OUR next example is to study the form and 

 structure of laticiferous vessels which may 

 be detected in all the papaveraceous plants, as well 

 as in Euphorbiaceoe, and in many Composite. The 

 specimen from which the illustration is taken is the 

 greater celandine [Chettdonium ma/us), a very com- 

 mon species found just outside villages and around 

 the hedges of old-fashioned gardens. Not unfre- 

 quently sections of the petiole and stem are made 

 on purpose to find the laticiferous vessels, but it 

 often ends in failure, from the mere fact that the 

 latex runs out of the vessel speedily when ruptured, 

 so it becomes difficult to trace successfully. By far 

 the better plan is to tear off the young sepals, laying 

 them on the slide, with a drop of water, then placing 

 on the cover slip, examine it as quickly as possible 

 for the vessels along the outer margin ; ' they are 

 readily recognised by the yellow juice. (Fig. 29. No. 

 1, margin of sep, ; 2, laticiferous vessel ; 3, -cellular 

 tissue.) 1 



Laticiferous vessels are simple or branched tubes, 

 frequently : tlni ted into a more or less close network, 

 as may be se,en in the lettuce leaf. The coloured 

 fluid is known as latex, which is valuable in many 

 cases, -as yielding gums and resins (opium, india- 

 rubber, Sec.) They occur in a comparatively small 

 number of plants, usually in the cortex, between the 

 xylerii and bast cells, sometimes in the outer bar 



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